A motor-driven type exposure adjusting device, such as a diaphragm-shutter device, adapted for a lens incorporating camera, an interchangeable lens, or the like. In the adjusting device, a rotary member has an optical path hole formed in a central portion thereof and is arranged to control the opening and closing actions of a plurality of light shielding blades. A stepping motor servers as a drive source for the rotation of the roatary member and is disposed outside of the optical path hole, and an aperture position detecting means detects a boundary between a given maximum aperture position defined by the light shielding blades and a stopped-down aperture position of the optical path hole. The aperture position of the optical path hole is detected through the rotating angle position of a rotary wheel to which the rotation output of the rotor shaft of the stepping motor is transmitted.