To prevent liquefied gas and wet vapor not vaporized at a low temperature from vaporizing by a temperature rise to increase the pressure of vaporized gas and cause an engine malfunction due to over-rich mixture, when injecting liquefied gas as vaporized gas of positive pressure by a fuel injection valve.

A regulator 2 has a heat exchanging mechanism 6 for vaporizing liquefied gas sent from a cylinder 1, and a pressure adjusting mechanism 5 for keeping vaporized gas in a pressure adjusting chamber 4 at a specified positive pressure. The regulator 2 opens a check valve 16 for discharging high pressure liquefied gas to a liquefied gas passage 11 and prevents mixture over- rich when the liquefied gas and the wet vapor not vaporized and remaining in the pressure adjusting chamber 4 and a vaporized gas passage 12 are vaporized by a temperature rise to increase pressure.