To provide a collision determination device capable of accurately determining collision within a short period of time without delay even in the case of a frontal collision with a collision body such as a narrow body.

First, second and third frequency separating sections 8, 9, 10 separate a high frequency component signal furnishing the plastic deformation information of a vehicle structural member and a low frequency component signal furnishing the deceleration information of a vehicle respectively from acceleration signals detected by first, second and third acceleration sensors 3, 4a, 4b. First and second collision determination sections 14, 15 determine the direction of the collision, the collision, and the magnitude of the collision from the high frequency component signal and low frequency component signal of the acceleration signals separated by the first and second collision determination sections 14, 15.