Motive power supply equipment for a natural gas liquefaction plant includes gas turbine equipment having a compressor for compressing air, a combustor for generating combustion gases by burning a fuel and the compressed air from the compressor, and a turbine rotated by the combustion gases from the combustor. A low-temperature heat source supply system is provided which, during rated load operation of the gas turbine equipment, supplies carbon dioxide as a cooling medium to the gas turbine equipment in order to cool the gas turbine equipment. The carbon dioxide supplied is generated by separation from the natural gas in the natural gas purification equipment.