A collision determination system of the present invention includes a plurality of acceleration sensors provided in a bumper face of a vehicle for detecting the acceleration of deformation of the bumper face when the vehicle collides with an object. The system also includes an actuation permitter which, even when one of the acceleration sensors detects an acceleration equal to or more than a set value and it is determined that a collision occurs, refers to another acceleration sensor for operation. Under the AND conditions that an actuation permitting signal is supplied from the actuation permitter and a collision detection signal is supplied from a collision detector, an actuating signal output outputs an actuating signal for actuating collision mitigating devices.