A diaphragm control apparatus is provided in a camera body, in which a controller drives a stepping motor to move the slider away from an origin position, thereafter drives the stepping motor in the opposite direction toward the origin position, and thereafter detects the slider position after holding the stepping motor for a first waiting time upon a distance from the slider to the origin position becoming less than slider-moving distance for one step of the stepping motor. The controller causes the stepping motor to enter a free state upon a lapse of the first waiting time and detects the slider position upon a lapse of a second waiting time to set an initial excitation pattern from a difference between the slider position detected during the first waiting time and the slider position detected in the free state thereof and from the moving distance of the slider.