PURPOSE: To forcibly discharge bubbles formed due to cavitation.

CONSTITUTION: Regarding the liquefied gas pump device where a pump chamber 40 with an inlet 34 and an outlet 52 is formed out of a piston 22 and a cylinder 21 to give a relative vertical motion for alternately performing intake and delivery strokes for delivering high-pressure liquefied gas, a bubble discharge port 50 formed separately from the inlet 34, so as to keep an upper end section in the chamber 40 communicated to the outside thereof in the initial stage of the delivery stroke. Also, a cutout section 49 extending upward is formed on an edge positioned at the upper side of the chamber 40, and the discharge hole 50 at the side of the chamber 40 is made open to the top of the section 49. The piston 22 is fixed and the cylinder 21 is driven vertically. In this case, the cylinder 21 may alternatively be fixed and the piston 22 made to reciprocate. Also, the discharge hole 50 is fitted with an open/close means to keep the temporary communication thereof at least during the initial stage of the delivery stroke and, then, the closure thereof.