The present invention discloses a digital single-lens reflex camera having a first mirror for reflecting part of a light beam coming from a subject through a photographing optical system and transmitting the remaining light beam. The reflected light beam is used for detecting the focus state of an imaging light beam, and the transmitted light beam is used for performing live view display. For example, the first mirror can be configured as a movable mirror in the digital single-lens reflex camera. This enables continuous live view display using the transmitted light beam on condition that the movable mirror is down while detecting the focus state using the reflected light beam. In addition, phase-contrast AF can be adopted for detecting the focus state.