Abstract: A hydraulic torque motor comprising a cylindrical housing (1), a piston (30) which can only be moved axially in the housing (1) and a rotor (20) which can only be rotated and which extends through the piston (39). The rotor (20) has a spiral groove (21) and the piston (30) has an engagement element (39) which extends radially inward in the groove (21). The piston (30) has a cylindrical section (31), each end of which has a circular end flange (34, 35), which abuts sealingly and slidingly against the housing's (1) boring. The housing (1) has a center flange (5) which projects radially inwards between the end flanges (34, 35) and is arranged to abut slidingly against the cylindrical piston section (31). The end flanges (34, 35) and the center flange (5) and those sections of the housing's (1) boring which are located between the flanged (5, 34, 35) define two cylinder spaces (37, 38).