PURPOSE: To prevent the increase of the length in the axial direction of a block by arranging a number of clutch valves which move in reciprocation between the inner and outer positions in the radial direction and short-circuit the inside and outside oil passages in the case when the troke becomes over a certain value, alternately with the second distribution valve, on a cylinder block.

CONSTITUTION: A number of clutch valves 62 which reciprocate between the inner and outer positions in the radial direction and short-circuit the inner and outer oil passages 52 and 53 when the reciprocation movement stroke exceeds a certain value are installed on a cylinder block B. The clutch valves 62 are arranged alternately in the radial direction and in the circumferential direction for the second distribution valve 61. The clutch valve 62 is engaged with the second eccentric wheel 64 together with the second distribution valve 61. The second eccentric wheel 64 can be moved so as to shift between a clutch-ON position for applying the ordinary reciprocation movement for the second distribution valve 61 and a clutch-OFF position for moving the clutch valve 62 in reciprocation to the short circuit position of both the oil passages 52 and 53. Accordingly, even if the clutch valve 62 is installed, the length in the axial direction of the cylinder block B is not increased, and the compact constitution can be obtained.