The height of the center of gravity of a stacker crane is determined in consideration of a height position of an elevation frame and the inertial force is determined from the travel acceleration and deceleration. Wheel pressures applied to front and rear drive wheels are determined based on the height of the center of gravity, the inertial force, and horizontal distances from the center of gravity to the front and rear drive wheels. Torques are allocated in proportion to the determined wheel pressures.