A first drive member which rotates with a rotor includes a first cam portion and a second cam portion, and a second drive member which connects a drive pin with a shutter blade includes a first cam portion and a second cam portion. A circular hole of the link member is fitted to a shaft member which is fixed to the first drive member and an elongated hole thereof is fitted to the shaft member fixed to the second drive member. The first drive member rotates the second drive member first via the link member and subsequently rotates the same directly so that when an abutting portion of the second drive member comes into abutment with an edge of the elongated hole, a generated repulsive force acts toward an axis of rotation of the first drive member irrespective of the direction of rotation of a rotor 7.