diff --git a/CHANGE.txt b/CHANGE.txt
index e9c1cdb..932a0d3 100644
--- a/CHANGE.txt
+++ b/CHANGE.txt
@@ -1,4 +1,12 @@
 更新履歴
+TAG021 2019/12/19
+  Core
+    ・o(オクターブ)、v(ボリューム)コマンドの修正
+    コマンドのみ記述したとき、前回使用した値が使用するように修正。
+    例)
+    　o4 c>c>coc  ->  o4 c>c>co4 c と同じ
+    　v15c(c(cvc  ->  v15c(c(cv15c と同じ
+
 TAG020 2019/12/03
   コマンドメモ
     ・soxのurlが間違っていたので修正。
diff --git a/Core/MMLAnalyze.cs b/Core/MMLAnalyze.cs
index 050f1af..0de0e38 100644
--- a/Core/MMLAnalyze.cs
+++ b/Core/MMLAnalyze.cs
@@ -434,17 +434,18 @@ private void CmdVolume(partWork pw, MML mml)
                 mml.type = enmMMLType.Volume;
                 mml.args = new List<object>();
 
-                if (!pw.getNum(out n))
+                if (pw.getNum(out n))
                 {
-                    msgBox.setErrMsg(msg.get("E05003"), pw.getSrcFn(), pw.getLineNumber());
-                    n = (int)(pw.MaxVolumeEasy * 0.9);
-                }
+                    //逶ｸ蟇ｾ髻ｳ驥剰ｪｿ謨ｴ
+                    n = n + pw.RelVolume;
 
-                //逶ｸ蟇ｾ髻ｳ驥剰ｪｿ謨ｴ
-                n = n + pw.RelVolume;
-
-                n = Common.CheckRange(n, 0, pw.MaxVolumeEasy);
-                mml.args.Add(n);
+                    n = Common.CheckRange(n, 0, pw.MaxVolumeEasy);
+                    mml.args.Add(n);
+                }
+                else
+                {
+                    mml.args = null;
+                }
             }
         }
 
@@ -478,17 +479,21 @@ private void CmdTotalVolume(partWork pw, MML mml)
         private void CmdOctave(partWork pw, MML mml)
         {
             pw.incPos();
-            if (!pw.getNum(out int n))
+            if (pw.getNum(out int n))
             {
-                msgBox.setErrMsg(msg.get("E05005"), pw.getSrcFn(), pw.getLineNumber());
-                n = 4;
-            }
-            n = Common.CheckRange(n, 1, 8);
+                n = Common.CheckRange(n, 1, 8);
 
-            mml.type = enmMMLType.Octave;
-            mml.args = new List<object>();
-            mml.args.Add(n);
-            pw.octaveNow = n;
+                mml.type = enmMMLType.Octave;
+                mml.args = new List<object>();
+                mml.args.Add(n);
+                pw.octaveNow = n;
+                pw.latestOctave = n;
+            }
+            else
+            {
+                mml.args = null;
+                pw.octaveNow = pw.latestOctave;
+            }
         }
 
         private void CmdOctaveUp(partWork pw, MML mml)
diff --git a/Core/chips/clsChip.cs b/Core/chips/clsChip.cs
index 49a8b95..d2a093e 100644
--- a/Core/chips/clsChip.cs
+++ b/Core/chips/clsChip.cs
@@ -900,8 +900,11 @@ public virtual void CmdTotalVolume(partWork pw, MML mml)
 
         public virtual void CmdVolume(partWork pw, MML mml)
         {
-            int n = (int)mml.args[0];
+            int n;
+            n = (mml.args != null && mml.args.Count > 0) ? (int)mml.args[0] : pw.latestVolume;
             pw.volume = Common.CheckRange(n, 0, pw.MaxVolume);
+            pw.latestVolume = n;
+
             SetVolume(pw);
         }
 
diff --git a/Core/chips/clsOPN.cs b/Core/chips/clsOPN.cs
index a27e717..3afefa5 100644
--- a/Core/chips/clsOPN.cs
+++ b/Core/chips/clsOPN.cs
@@ -1218,9 +1218,10 @@ public override void CmdEnvelope(partWork pw, MML mml)
 
         public override void CmdVolume(partWork pw, MML mml)
         {
-            int n = (int)mml.args[0];
-            n = Common.CheckRange(n, 0, 15);
+            int n;
+            n = (mml.args != null && mml.args.Count > 0) ? (int)mml.args[0] : pw.latestVolume;
             pw.volumeEasy = n;
+            pw.latestVolume = n;
             if (pw.Type == enmChannelType.FMOPN || pw.Type == enmChannelType.FMOPNex)
             {
                 n = FMVDAT[n + 4];
diff --git a/Core/partWork.cs b/Core/partWork.cs
index 6de2e62..fdc33a8 100644
--- a/Core/partWork.cs
+++ b/Core/partWork.cs
@@ -128,6 +128,8 @@ public class partWork
 
         public int octaveNew = 4;
 
+        public int latestOctave = 0;
+
         public int TdA = -1;
         public int op1ml = -1;
         public int op2ml = -1;
@@ -145,6 +147,8 @@ public class partWork
         /// </summary>
         public int volume = 0;
 
+        public int latestVolume = 0;
+
         /// <summary>
         /// 邁｡譏薙�懊Μ繝･繝ｼ繝�
         /// </summary>