Index: lucene/CHANGES.txt
===================================================================
--- lucene/CHANGES.txt	(revision 1477914)
+++ lucene/CHANGES.txt	(working copy)
@@ -388,6 +388,8 @@
 * LUCENE-4937: Fix incorrect sorting of float/double values (+/-0, NaN).
   (Robert Muir, Uwe Schindler)
 
+* LUCENE-4970: Fix boost value of rewrited NGramPhraseQuery. (Shingo Sasaki)
+
 Documentation
 
 * LUCENE-4841: Added example SimpleSortedSetFacetsExample to show how
Index: lucene/core/src/java/org/apache/lucene/search/NGramPhraseQuery.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/search/NGramPhraseQuery.java	(revision 1477914)
+++ lucene/core/src/java/org/apache/lucene/search/NGramPhraseQuery.java	(working copy)
@@ -64,6 +64,7 @@
 
     // now create the new optimized phrase query for n-gram
     PhraseQuery optimized = new PhraseQuery();
+    optimized.setBoost(getBoost());
     int pos = 0;
     final int lastPos = terms.length - 1;
     for(int i = 0; i < terms.length; i++){
Index: lucene/core/src/test/org/apache/lucene/search/TestNGramPhraseQuery.java
===================================================================
--- lucene/core/src/test/org/apache/lucene/search/TestNGramPhraseQuery.java	(revision 1477914)
+++ lucene/core/src/test/org/apache/lucene/search/TestNGramPhraseQuery.java	(working copy)
@@ -88,6 +88,17 @@
     pq3 = (PhraseQuery)q;
     assertArrayEquals(new Term[]{new Term("f", "ABC"), new Term("f", "DEF"), new Term("f", "FGH")}, pq3.getTerms());
     assertArrayEquals(new int[]{0, 3, 5}, pq3.getPositions());
+    
+    // boosting test
+    PhraseQuery pq4 = new NGramPhraseQuery(2);
+    pq4.add(new Term("f", "AB"));
+    pq4.add(new Term("f", "BC"));
+    pq4.add(new Term("f", "CD"));
+    pq4.setBoost(100.0F);
+    
+    q = pq4.rewrite(reader);
+    assertNotSame(pq4, q);
+    assertEquals(pq4.getBoost(), q.getBoost(), 0);
   }
 
 }