I believe this to be an A-II model, first introduced in 1954.
The Twin Lens Reflex (TLR) had gained popularity between the wars due in large part to the German Rolleicord models, much loved by press photographers. They were relatively light and simple, compared to cumbersome plate cameras that had preceded them.
This TLR represents the first cameras to be made under the Yashica brand name, it having been established a few years after the end of WWII as part of Japan’s industrial recovery. After a few years of clock component manufacture, the nascent Yashica company turned it’s efforts to camera production.
In common with most TLR’s, this model has a “sports finder” mode, whereby the front part of the viewfinder folds down and the user can attempt to compose by peering through what amounts to rifle sights. There’s also a flip up magnifier to try and help with focusing. The composing lens is pretty dim, and the magnifier does help somewhat.