A fuel supply apparatus of a liquefied gas carrier includes: a compressor for compressing gas fuel into a high pressure; a compressed gas storage tank being filled with the compressed high-pressure gas fuel, for storing the gas fuel; and a decompressor for decompressing the high-pressure gas fuel drawn from the compressed gas storage tank into a pressure suitable to be used in a propulsion system, to supply fuel to the propulsion system. The gas fuel is at least one of a natural boiled-off gas which is naturally evaporated in the cargo tank, a forced boiled-off gas which is artificially evaporated, and a gas additionally supplied for the use of fuel. Further, the compressor is a multistage high-pressure compressor and the decompressor is a multistage decompressor.