PURPOSE: To constitute steering linkage by a steering wheel so as to selected to front-wheel steerage from rear-wheel steerage and thereby perform a changeover between the front-wheel steerage and the rear-wheel one simply and accurately by moving the steering wheel to the lateral side.

CONSTITUTION: When a steering wheel 1 is set to each of symmetrical central parts, a shifter arm 26 and a shifter 22 are operated via two wires 24, 25, and each of clutches 16, 17 in front and in the rear are moved. If so, a pin hole 30 of this front clutch 16 is removed from a lock pin 27, while it is engaged with a spline shaft 14, thereby steering a front-wheel steering shaft 18. Then, the rear clutch 17 is separated from a mesh with the spline shaft 14, and it interrupts its steering linkage with a rear-wheel steering shaft 19, while it makes a pin hole 31 fit in a lock pin 28, locking the rear-wheel steering shaft 19 into being unrotated, thus rear wheels are kept in a rectilinear steering position. On the other hand, when the steering wheel 1 is moved to the lateral side, only the rear wheels are steered.