An exposure control unit including an element having electrostrictive properties and a fixed end and a deformation quantity of which is determined in accordance with a voltage applied thereto drives a programming shutter provided with shutter blades having the function of the diaphragm by a driving source composed of the deformation produced at a free end of the electrostrictive element when the voltage is applied to the element. The shutter blades having the function of the diaphragm are opened by the deformation produced at the free end of the electrostrictive element in accordance with the voltage applied to the element and the voltage is increased with the lapse of time in interlocked relationship with the opening operation of the shutter blades so that the electrostrictive element is gradually deformed and the shutter blades are also gradually opened. The electrostrictive element is then short-circuited at a time when a proper exposure is obtained so that the exposure operation is immediately terminated.