A sector drive assembly for a camera which can open and close an aperture has a sector drive unit having an actuator, a drive force transmitting mechanism, and a sector position detecting unit that are removably mounted as a unit to a support plate, and a sector unit having a base plate formed with an aperture and one or more sectors for opening and closing the aperture. Since the sector drive unit is provided as a removably mountable unit, it is high in versatility and can be mounted to various different types of sector units. In addition, since it is configured to detect the state of the sectors before operation, reliable exposure or opening and closing of the aperture are achieved. In addition, a positional adjustment function is provided by a sector urging spring.