A slit exposure shutter having the front and rear screens thereof respectively arranged to be driven by a source of an electromagnetic driving force is provided with a minimum slit width insuring means which prevents uneven exposure resulting from difference in travelling speed between the front and rear shutter screens during a high speed shutter operation and particularly prevents a total absence of the slit, the shutter is also provided with a nullifying means which nullifies the insuring means when the shutter screens are on their return travels.