According to the present invention, light from a taking lens is reflected by a quick return mirror in a lateral direction of a body unit. Then, after passing through a screen, the light is reflected toward an upper side of the body unit by a second mirror except part of the light. The light reflected by the second mirror is reflected by a third mirror in a direction opposite to a direction in which the light is reflected by the quick return mirror, and is further reflected by a fourth mirror toward an eyepiece located on a back side of the body unit. Part of the light which passing though the screen is taken by an AF sensor unit provided in rear of the second mirror, and an image formation position of an optical image is detected.