An annular piston (21) is inserted into a cylinder hole (20) of a housing (4) so as to be vertically movable and be prevented from rotating. Into a cylindrical hole (24) of the piston (21), a cylindrical rotating member (25) is inserted while prevented from moving vertically. A ball screw mechanism (28) is provided between the piston (21) and the rotating member (25). On an outer peripheral surface of the rotating member (25), a circulation passage (59) which communicatively connects a start end and a terminal end of a male spiral groove (56) is formed in a recessed manner. Into a guide hole (29) formed in an upper half of the housing (4), an output rod (30) is inserted rotatably and movably vertically. An input portion (41) of the output rod (30) is connected to the rotating member (25) so as to transmit rotation. By driving the piston (21) upward, a bolt (45) provided on an upper end portion of the output rod (30) is engaged with an internal threaded hole (12) of a work (10).