To enable rapid-focusing, and also, to simplify an internal constitution, as for a digital still camera.

A mirror box 27 through which light reaching a CCD 40 after being emitted from a photographing optical system 13 passes is formed in the camera main body 20 of the digital still camera 10, and an AF unit 30 is arranged at the bottom part of the camera main body 20. A half mirror 26 is arranged at 45° to the optical axis E in the mirror box 27. And, the size of the half mirror 26 is fixed so that all the light reaching the photosensor area of the CCD 40 may pass through the mirror 26. When the light from an object is made incident on the photographing optical system 13, the incident light is guided by the half mirror 26 to the AF unit 30 and the CCD 40.