A collision detecting system for a vehicle has a pressure detecting member for detecting a pressure in a substantially closed space which is arranged at a periphery portion of the vehicle, and a vibration detecting member for detecting a vibration of the vehicle. The pressure in the space is calculated for a detection of a vehicle collision, based on pressure signals detected by the pressure detecting member and vibration signals detected by the vibration detecting member. Therefore, the influence of the vehicle vibration on the detection of the pressure in the space can be restricted, thus improving the detection of the vehicle collision.