The mirror device of a single-lens reflex camera according to the present invention includes a main mirror section having a reflecting mirror surface that moves to a first position for reflecting an object beam to an observation optical system and to a second position retracted from the object beam, a sub-mirror section having a reflecting mirror surface located, in conjunction with movement of the main mirror section, at a position apart from the main mirror section when the main mirror section is located at the first position and at a position retracted from the object beam together with the main mirror section when the main mirror section is located at the second position, and a cushioning section interposed between the sub-mirror section and the main mirror section when the main mirror section moves from the first position to the second position.