An electromagnetic diaphragm shutter mechanism is provided with an electromagnet in the form of a coil or a printed circuit pattern arranged on a sector ring of the shutter mechanism. With a magnetic field applied to the electromagnet, when current is caused to flow therethrough in a prescribed direction, the sector ring is driven to rotate. A light measuring diaphragm mechanism related to the exposure diaphragm of the shutter blades serves to control the shutter and to improve the accuracy of program control of the shutter, the sector ring being always urged to move in a direction to close the shutter.