Mizuho

Mizuho was a Japanese company that made some 6×6 folders in the 1950s. According to this page at Japan Family Camera, its full name was Mizuho Kōki Seisakusho (ミヅホ光機製作所) and it later became Neoca.

Note: According to this AJCC page, Mizuho was written ミヅホ on period advertisings, not ミズホ.