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.