diff --git a/src/main/java/org/codelibs/fess/thumbnail/ThumbnailManager.java b/src/main/java/org/codelibs/fess/thumbnail/ThumbnailManager.java
index c5dde96e1..6f8770468 100644
--- a/src/main/java/org/codelibs/fess/thumbnail/ThumbnailManager.java
+++ b/src/main/java/org/codelibs/fess/thumbnail/ThumbnailManager.java
@@ -211,20 +211,24 @@ public class ThumbnailManager {
             idList.add(entity.getId());
             final String generatorName = entity.getGenerator();
             try {
-                final ThumbnailGenerator generator = ComponentUtil.getComponent(generatorName);
                 final File outputFile = new File(baseDir, entity.getPath());
                 final File noImageFile = new File(outputFile.getAbsolutePath() + NOIMAGE_FILE_SUFFIX);
                 if (!noImageFile.isFile() || System.currentTimeMillis() - noImageFile.lastModified() > noImageExpired) {
                     if (noImageFile.isFile() && !noImageFile.delete()) {
                         logger.warn("Failed to delete " + noImageFile.getAbsolutePath());
                     }
-                    if (!generator.generate(entity.getThumbnailId(), outputFile)) {
-                        new File(outputFile.getAbsolutePath() + NOIMAGE_FILE_SUFFIX).setLastModified(System.currentTimeMillis());
-                    } else {
-                        final long interval = fessConfig.getThumbnailGeneratorIntervalAsInteger().longValue();
-                        if (interval > 0) {
-                            Thread.sleep(interval);
+                    final ThumbnailGenerator generator = ComponentUtil.getComponent(generatorName);
+                    if (generator.isAvailable()) {
+                        if (!generator.generate(entity.getThumbnailId(), outputFile)) {
+                            new File(outputFile.getAbsolutePath() + NOIMAGE_FILE_SUFFIX).setLastModified(System.currentTimeMillis());
+                        } else {
+                            final long interval = fessConfig.getThumbnailGeneratorIntervalAsInteger().longValue();
+                            if (interval > 0) {
+                                Thread.sleep(interval);
+                            }
                         }
+                    } else {
+                        logger.warn(generatorName + " is not available.");
                     }
                 } else if (logger.isDebugEnabled()) {
                     logger.debug("No image file exists: " + noImageFile.getAbsolutePath());
@@ -291,6 +295,7 @@ public class ThumbnailManager {
     }
 
     public void add(final ThumbnailGenerator generator) {
+        logger.info(generator.getName() + " is available.");
         if (generator.isAvailable()) {
             generatorList.add(generator);
         }
diff --git a/src/main/java/org/codelibs/fess/thumbnail/impl/BaseThumbnailGenerator.java b/src/main/java/org/codelibs/fess/thumbnail/impl/BaseThumbnailGenerator.java
index 4e8fa24ba..e545f6480 100644
--- a/src/main/java/org/codelibs/fess/thumbnail/impl/BaseThumbnailGenerator.java
+++ b/src/main/java/org/codelibs/fess/thumbnail/impl/BaseThumbnailGenerator.java
@@ -59,6 +59,8 @@ public abstract class BaseThumbnailGenerator implements ThumbnailGenerator {
 
     protected int maxRedirectCount = 10;
 
+    protected Boolean available = null;
+
     public void addCondition(final String key, final String regex) {
         final String value = conditionMap.get(key);
         if (StringUtil.isBlank(value)) {
@@ -84,6 +86,9 @@ public abstract class BaseThumbnailGenerator implements ThumbnailGenerator {
 
     @Override
     public boolean isAvailable() {
+        if (available != null) {
+            return available;
+        }
         if (generatorList != null && !generatorList.isEmpty()) {
             String path = System.getenv("PATH");
             if (path == null) {
@@ -97,7 +102,7 @@ public abstract class BaseThumbnailGenerator implements ThumbnailGenerator {
             if (path != null) {
                 stream(path.split(File.pathSeparator)).of(stream -> stream.map(s -> s.trim()).forEach(s -> pathList.add(s)));
             }
-            return generatorList.stream().map(s -> {
+            available = generatorList.stream().map(s -> {
                 if (s.startsWith("${path}")) {
                     for (final String p : pathList) {
                         final File f = new File(s.replace("${path}", p));
@@ -110,8 +115,10 @@ public abstract class BaseThumbnailGenerator implements ThumbnailGenerator {
                 }
                 return s;
             }).allMatch(s -> new File(s).isFile());
+        } else {
+            available = true;
         }
-        return true;
+        return available;
     }
 
     @Override
diff --git a/src/main/java/org/codelibs/fess/thumbnail/impl/EmptyGenerator.java b/src/main/java/org/codelibs/fess/thumbnail/impl/EmptyGenerator.java
index f5530c8e1..f64ff9c5d 100644
--- a/src/main/java/org/codelibs/fess/thumbnail/impl/EmptyGenerator.java
+++ b/src/main/java/org/codelibs/fess/thumbnail/impl/EmptyGenerator.java
@@ -28,9 +28,4 @@ public class EmptyGenerator extends BaseThumbnailGenerator {
     public void destroy() {
         // nothing
     }
-
-    @Override
-    public boolean isAvailable() {
-        return true;
-    }
 }