To allow a lockout state to be an overriding state by a control unit temporarily by making a lockout state in response to the signal of a sensor for detecting and indicating an operation state, and also making the lockout state into an overriding state selectively in terms of an overriding signal and sensor signal.

In a skid steer loader, for instance, as a seat bar connected rotatably to a part of an operation chamber is situated at an elevation position, a control unit 44 controls a traction lockout mechanism 58 and liquid pressure lockout mechanism 60 so as to lock the traction, elevation and inclination function of a loader. In addition, a push operation (PTO) switch 52 works to make a traction lockout state assigned by the control unit into an overriding sate in response to a signal from a seat bar sensor 48 utilizing a Hall effect indicating that the seat bar stays at an elevation position. Accordingly, a traction effect lock state (a lock state of a driving mechanism 66 is locked) can readily be made into an overriding state only by pushing a button 52 by the operator.