The light-amount adjusting system includes a light-amount adjusting unit that changes a size of an aperture through which light passes, an actuator that drives the light-amount adjusting unit, and a detector that detects an aperture state of the light-amount adjusting unit. When an input signal is given, a feature conversion unit calculates a feature and a sound pressure of the input signal. As the object moves, the cable is would or unwound about the spool and the spool rotates in direct correlation to the movement of the object.