returned to the oil tank through the through hole 42 the displacement of the piston head 40 and the piston rod 36 is then interrupted and subsequently the piston head 40 is returned to its original position by the spring 33 during this returning displacement of the piston head 40 toward the left the flange part 35b is held separated from the piston head 40 by the spring 43 so that the returning displacement is performed smoothly fig3 is a partial sectional view illustrating still another embodiment of the hydraulic cutter of the present invention it shows the valve mechanism part as in fig2 in this embodiment a valve body 44 in the form of a plate is slidably fitted to a guide bar 46 axially protruding from the inner wall of a cylinder 45 the guide bar 46 is inserted in a central hole 47a formed in a piston rod 47 and a bolt 49 for securing a spring 48 is screwed to the front end of the guide bar 46 the oil releasing path is defined as in the case of the embodiment shown in fig2 by the through hole 41 formed in the piston head 40 and the through.