Judging by my source "Standard Catalog of Military Firearms" (7th Edition) by Phillip Peterson, this seems to be a later model (by the large trigger guard) Type 14 Nambu Pistol. On the right side of the receiver (below the serial number) you'll see the numerals "16.6". This means that the gun was produced in the 16th year of Hirohito's reign during the sixth month, or 1941-June. Approximately 73,000 of these (large trigger guard) Nambu t-14 pistols were made between 1939 and 1945.
Hope this helps!