A determination device includes a single acceleration sensor that measures an acceleration of a vehicle and a determination circuit that is electrically connected with the acceleration sensor. The determination circuit has a plastic deformation pulse detection section and a severity determination section. The plastic deformation pulse detection section detects a plastic deformation pulse by separating the plastic deformation pulse from an acceleration waveform produced by the acceleration sensor. The severity determination section determines severity of a collision in a vehicle accident based on the detected plastic deformation pulse. A passive safety device is operated according to the determined severity.