PURPOSE: To stabilize the behavior of a vehicle by shutting off an actuator driving power source by a command to a relay circuit when an abnormality is detected in a transmission torque control system, and controlling the opening area of a variable orifice so that a specific low transmission torque characteristic is obtained when an abnormality is detected in an input information system.

CONSTITUTION: When an abnormality is detected in a transmission torque control system by a detecting means (f), a first fail-safe control means (g) outputs a command for shutting off a driving power source to a relay circuit (e), a rotational difference sensing joint (c) releases controlling force for an actuator (a) to operate a variable orifice (b) so as for a maximum opening area to be obtained, and the opening area is secured to the characteristic on the safety side which generates a minimum transmission torque in relation to a relative rotation difference. When an abnormality is detected by an input information system abnormality detecting means (i), a second fail-safe control means (j) outputs a control command for the orifice opening area which generates a weak transmission torque in relation to the relative rotational difference to a transmission torque control means (h), and thus the characteristic having some joint performance on the safety side is obtained. The behavior of a vehicle is thus stabilized.