Abstract: A finder device is disclosed in which a finder optical system is provided with an auto-focus function separate from that of a photographic optical system so that the subject image can be observed sharply even when the finder optical system undergoes a change of state due to temperature and other causes. A semitransparent mirror is interposed between an objective lens system and an erecting optical system to branch out a focus detection system optical path from a finder system optical system. A focus detection device is arranged on the focus detection system optical path so that its focus detection plane is situated at the equivalent position to the focal plane of the finder. The state of focus is obtained from the subject image formed on the focus detection plane by using a phase difference detection system or the like. Driving means moves a focus lens system forward/backward along the optical axis so that the subject image focuses on the focus detection plane.