PURPOSE: To sharply shorten an overall height and an overall length and to improve safety through lowering of a center of gravity.

CONSTITUTION: The upper end of a stay 23 erected on a main base 22 is fixed to an auxiliary base 24. A pressure cylinder 26 is fixed to a main base 22 in a state that a ram 25 is pointed to the auxiliary base side, and a reaction force receiving member 28 is arranged to the stay 23 above the main base in a state to be movable along the stay. The upper end of the rod of an auxiliary cylinder 27 erected to the side of the pressure cylinder is connected to the reaction force receiving member and a lock groove 34 is formed in the stay. A locking mechanism 29 to bring the reaction force receiving member into an immobile state from the stay when the engaging member 35 is engaged with the lock groove is arranged to the reaction force receiving member.