To provide a detecting means capable of accurately measuring the connection angle with a simple structure at a low cost in a behavior control device for connected vehicles for detecting the connection angle of a towing vehicle and a towed vehicle as a parameter.

This detecting means of the connection angle is provided with an arm 9 turnable around the connection point of the towing vehicle and the towed vehicle 2 on one of them and a means 8 generating the output corresponding to the turn angle position, and the free end of the arm 9 is supported via a fixed point 11 set on the other. An elastic expanding/shrinking means 10 allowing the relative rotation exceeding the detection range of the connection angle of the towing vehicle and the towed vehicle 2 is provided as a portion of the arm 9.