Mizuho Automobile Manufacturing Co., Ltd, Inuyama City, Aichi Prefecture, 1923-56
Mizuho is probably much better known as Cabton, which is the line of machines they built between 1923 and 1956 with a gap in production during WWII. The bikes generally looked like British models and had displacements ranging from 350cc to 600cc. Mizuho also supplied engines to other manufacturers in the early 1950's (for example, see Arai).
Not surprizingly Cabton appeared in several films including the original 1954 Japanese language version of Godzilla (reference this link on imcbd.org).
Mizuho also built a line of machines under their own name although at this point I'm not sure for which years. Possibly just post WWII between 1953 and 1955.