To enable a heating time for hot water to be shortened and further enable heating of liquefied natural gas to be carried out from an early time. SOLUTION: There are provided a gas heating device 4 arranged in the midway part of a gas pipe 2 for reducing pressure of liquefied natural gas 1 and feeding it and for heat exchanging between the liquefied natural gas 1 and hot water 8; a hot water tank 25 provided with a steam heater 6; a circulating pipe 9 provided with a feeding pipe 9a and a return pipe 9b for circulating hot water 8 in the hot water tank 25 to the gas heating device 4; and an electrical heater 26 mounted at a feeding pipe 9a of the circulating pipe 9.