An occupant protecting device for a motor vehicle, which inflates an air-bag system reliably to protect occupants in the event of a collision with high reliability. The occupant protecting device includes an acceleration sensor for sensing an acceleration signal of a vehicle in the event of collision with another vehicle or the like, a signal processor for detecting a collision waveform from an acceleration signal output from the acceleration sensor, a comparator for determining whether or not the output signal of the signal processor exceeds a preset level to produce a trigger signal when it exceeds the preset level, a latch circuit for latching the trigger signal from the comparator, and a firing circuit for operating an occupant protecting unit in response to a drive signal from the latch circuit.