A mirror box includes a mirror that is selectively set to one of a reflecting position, which is on an optical path between a photographing lens and an imaging device so that incident light passing through the photographing lens is reflected to a view-finder, and a retracted position, which is out of the optical path so that said incident light is led to the imaging device. A filter is selectively set to one of a non-functioning position, which is close to the mirror, when the mirror is set to the reflecting position, and a functioning position, which is on the optical path so that a predetermined light component contained in the incident light is blocked, when the mirror is set to the retracted position. The filter comprises an optical low-pass filter, and the mirror comprises a half-mirror which is integrally provided on an incident surface of the optical low-pass filter.