A mirror driving device includes a positioner in the imaging apparatus; a mirror holder configured to hold the movable mirror and move to the first position and the second position of the movable mirror; a positioning surface at the mirror holder and configured to come into contact with the positioner to determine the first position of the movable mirror; and a shock dispersion surface provided at the mirror holder. When moving from the second position toward the first position, the movable mirror is configured to contact the positioner before the positioning surface comes into contact with the positioner to reduce a shock. The shock dispersion surface has a smaller inclination with respect to a travel-direction tangent line than an inclination of the positioning surface with respect to the tangent line. The shock dispersion surface is located forward of the positioning surface in the travel direction toward the first position.