In an imaging apparatus including a stepping motor that drives a diaphragm, a favorable moving image exposure control is carried out while reducing electrical power required for holding the diaphragm position. When a rotor and the magnetic poles of a stator do not face each other in a first mode, a control unit of the stepping motor drives the rotor to a facing position, and shuts off the current in a coil. When the diaphragm driving does not occur in a second operation mode, the control unit shuts off the current in the coil at the state where the rotor of the motor and the magnetic poles of the stator face each other. A holding current to be supplied to the motor is shut off in the first and second. The program profile of a diaphragm drive method and an exposure control is switched depending on the type of an imaging lens unit.