A sector drive unit for a camera includes sectors capable of opening and closing an aperture provided on a base plate. A first actuator drives the sectors to open and close the aperture, and a drive force transmitting mechanism transmits a driving force of the first actuator to the sectors. A sector retaining unit retains the sectors at the aperture-opening position or at the aperture-closing position, and a second actuator drives the sector retaining unit to a position to retain the sectors and to a position not to retain the sectors. The sector retaining unit prevents the sectors from moving accidentally due to an impact or the like when the sectors are at either the opened position or the closed position. The use of the second actuator for driving the sector retaining unit reduces power consumption and prevents generation of noise during the time of an exposure.