A steering rear axle (5) of a fork lift truck is swingable about a longitudinal swing shaft (9). Even with an ignition key (89) on, if an operation switch (88) is off, an electromagnetic switch valve (83) is de-energized, holding a port-connecting valve position (C) allowing hydraulic oil to be supplied from a hydraulic line (79) via the electromagnetic switch valve (83) and a hydraulic line (49) to a driving hydraulic cylinder (31), so that a slider (23) abuts on a stopper member (19), restricting a swing action of the steering axle (5). With the operation switch (88) turned on, the electromagnetic switch valve (83) is energized, having a port-connecting valve position (D) interrupting a hydraulic oil supply to the driving hydraulic cylinder (31), causing the slider (23) to depart from the stopper member (19), enabling the swing action of the steering axle (5).