The disclose circuit energizes a magnetic winding of a shutter actuating device. A constant voltage circuit is connected across the magnetic winding, or between the power supply terminal of the magnetic winding and a basic potential to ensure that the response of the armature of the actuating device to the output of a timing circuit is stabilized despite variation in the voltage of an electrical power source. This produces the advantage of substantially improving the accuracy of exposure control, because the closing operation of the shutter is controlled through movement of the armature.