To prevent contact and collision of the advancing side edge of a slit-like inflow passage opening to the ram front end without reducing a clearance more than needs.

A ram 16 reciprocating in a ram cylinder 14 is formed into an approximately hollow shape having the opening front end, the front end 16b of the ram 16 is positioned beyond the advancing side edge 38a of an opening of a slit-like inflow passage 38 communicated with the peripheral wall surface of the ram cylinder 14 in the advancing direction even in the retracting limit position. A suction ports 54 for sucking oil from the slit-like inflow passage 38 to the ram cylinder 14 has the axial length so as to be partially aligned to the inflow passage opening to the retracting limit position of the ram 16 and so as not to be aligned to the inflow passage opening in the advancing limit position of the ram 16, and it is formed on the hollow part side surface of the ram 16.