The present invention relates to a ship capable of running selectively with a liquefied fuel gas main drive engine and a liquefied fuel gas generator engine. The ship includes: a high pressure gas injection engine using liquefied fuel gas as the fuel gas for obtaining the thrust power of the ship; a generator engine using the liquefied fuel gas as the fuel gas for generating electricity; and a thrust body for driving the ship. The high pressure gas injection engine and the generator engine are alternatively power-connected to the thrust body so as to obtain the thrust power of the ship. According to this configuration, the ship is provided with the liquefied fuel gas main drive engine and the liquefied fuel gas generator engine, and obtains the thrust power by the liquefied fuel gas generator engine at low output, thereby saving fuel costs and solving environmental problems.