PURPOSE: To make the tilt down speed faster than the tilt speed by connecting a cylinder room at the piston rod non-housing side to a reservoir through a bypass duct and inserting in the said duct, a switching device that opens by the working pressure of a hydraulic pump at the tilt down.

CONSTITUTION: A pump 33 is rotated forward at the tilt up. The exhaust oil of the pump 33 flows into the room 38 of a main switching device 34 from a duct 42 and moves a piston 35 right. A check valve 37 is opened by the right movement of the piston 35. The exhaust oil of the pump 33 flows into the second room 22 of a tilt cylinder 18 through a duct 44 and the cylinder 18 is extended and then tilt up is performed. Besides, the pump 33 is rotated backward at the tilt down. The piston 35 moves left and a check valve 36 is opened. Furthermore, the exhaust oil of the pump 33 moves the piston 55 of an auxiliary switching device 54 and a check valve 56 is opened. Consequently, the pressurized liquid in the second room 22 returns to a reservoir 31 through a bypass duct 53. As a result, the contraction speed of the cylinder 18 is made faster than that at expansion and tilt down is performed quickly.