PURPOSE: To prevent a vehicle such as a fork lift truck or the like from tumbling upon turning and improve vehicle turning speed, by detecting a turning action of the vehicular body owing to a centrifugal force created upon turning of the vehicle, and locking an axle fixing mechanism.

CONSTITUTION: When a centrifugal force applied to a body of a fork lift truck upon turning thereof is detected by a vehicular turn detecting means (not shown) consisting of a magnetic rocking member and a generating element, signal S1 is inputted to a control circuit 19. The control circuit 19 outputs a lock operation signal S2 to a solenoid 28 of an axle fixing mechanism to operate a solenoid valve 27, which in turn switches a port 27a on a communication side and a port 27b on a interception side to supply oil pressure to a lock cylinder 22 and thereby to project a rod 24 for biasing against a rear axle 3 and fixing same. With this constitution, as the axle of the vehicle is automatically fixed upon turning, the vehicle may be prevented from tumbling upon turning and vehicle turning speed may be increased.