To provide a side collision detecting device for vehicle which can detect a collision with the side of a vehicle at a high accuracy, and can be realized at low cost.

A collision processing device 1 is composed by including n numbers of piezoelectric plate sensore s1 to sn to detect the deflection generated by the deformation of the side surface in the case of a collision of the side surface of a vehicle, and to output signals according to the deflecting amounts; signal processing circuits a1 to an to process the outputs of the piezoelectric plate sensors s1 to sn, and to output them to a central processing device 2; and the central processing device 2 furnishing a deciding means 3 and an analog/ digital converter 4. The deciding means 3 calculates an operation value by carrying out a preset operation, and when the operation value is a preset threshold value or higher, it is decided a collosion is generated.