The present invention relates to a gas apparatus comprising a high-pressure gas injection engine; an LNG storage tank (1); a fuel gas supply line (L1) connected from the LNG storage tank (1) to the high-pressure gas injection engine; a compressing means installed in the fuel gas supply line (L1) so as to extract LNG from the LNG storage tank (1), compress the extracted LNG, and supply the compressed LNG to the high-pressure gas injection engine; and a gasifying means (5) installed downstream of the compressing means in the fuel gas supply line (L1), so as to gasify the compressed LNG, wherein the high-pressure gas injection engine is an internal combustion reciprocating piston engine of an LNG vessel carrier; the gas apparatus is configured to be arranged in the LNG vessel carrier; the compressing means comprises a high-pressure pump to meet the fuel gas pressure requirements for the high-pressure gas injection engine; and extracted LNG is compressed at a high-pressure, gasified, and then supplied to the high-pressure gas injection engine.