From a collision load, a one-time integration value and a two-time integration value are computed. The one-time integration value and two-time integration value are then used for obtaining a mass and rigidity of a collision object as two primary parameters. The obtained two primary parameters are used for determining whether or not the collision object is a pedestrian. This achieves accuracy in determining the collision object that is remarkably superior to a conventional method that uses a collision load waveform.