To provide a breakdown detection device for an occupant protecting device capable of reducing burden of a user by improving accuracy in detecting breakdown.

This breakdown detection device of an occupant protecting device comprises a safing acceleration sensor 13 in an on-condition when acceleration over a predetermined threshold is applied, and a microcomputer 12 generating alarms by judging shortcircuit failure of the safing acceleration sensor when the on-condition of the safing acceleration sensor 13 continues for more than a predetermined shortciruit breakdown detecting time. The shortcircuit breakdown detecting time is set to exceed a time for generating acceleration of more than a predetermined threshold due to rapid change of the movement of a vehicle including rapid deceleration and spinning.