A digital camera includes a mirror box having a lens mount to which a photographing lens is mounted; an image pick-up device having an imaging surface for capturing an object image which is focused on the imaging surface through the photographing lens; and a frame positioned inside the digital camera body, the mirror box and the image pick-up device being mounted to the frame. The mirror box is mounted to a surface of the frame. The image pick-up device is mounted to the surface of the frame via at least one support member positioned between the mirror box and the image pick-up device. A ratio of a distance from the lens mount to the frame and a length of the support member is substantially equal to a ratio of a linear expansion coefficient of the support member and a linear expansion coefficient of the mirror box.