A collision detecting device for a motor vehicle for detecting a collision with a pedestrian has a pressure measuring chamber, which is formed by a tube, and a flexurally stiff structural element. The tube is formed to be deformable in the event of a collision, i.e. as a result of a collision of the motor vehicle with the pedestrian, and is correspondingly arranged. The tube is also supported in a direction, in particular in precisely one direction transverse to a vertical direction of the motor vehicle. In addition, the tube is essentially in particular flexurally stiffly supported on the structural element in precisely one, i.e. in exclusively one, vertical direction of the vehicle.