NAMBU:
Comparing your photo with the one I have, your NAMBU is the Model "B" or baby Nambu.
Which was developed concurrently with the larger Model "A", apparently for purchase by senior officers as a badge of rank. Made to the same general design as the Model "A", but somwhat smaller, it chambered a 7mm bottle necked cartridge. Production began about 1909-10 in Koishikawa arsenal, continuing until the early part of 1923. It is beleived that work was then transferred to the Tokyo Gas & Electric Co, where about 500 more were made. Early Model "B" guns had wooden magazine buttoms, a pinched in-cocking knob and a single diameter firing pin. After about 450 had been made, the magazine base became aluminium and the cocking knob was rounded and the multiple diameter firing pin was used. the Baby Nambu never achieved the popularity that had been hoped for, since it was almost twice the price of comparable importe pistols.