A liquefied natural gas, LNG, power plant comprising: a gas turbine power generation unit having a gas turbine and a power generator; an LNG vaporization facility configured to feed vaporized LNG as a fuel gas to the gas turbine power generation unit, wherein the LNG vaporization facility has a plurality of LNG storage tanks, the LNG storage tanks are connected to a common boiled off gas, BOG, compressor through respective BOG outlet valves, the LNG storage tanks are connected to a common vaporizer through respective boost pumps; a gas feed pipe extending from the BOG compressor and the vaporiser of the LNG vaporization facility to the gas turbine power generation unit; a fuel gas heating/cooling device disposed between the LNG vaporization facility and the gas turbine unit on the gas feed pipe, configured to heat and cool the fuel gas introduced into the gas turbine power generation unit; a heating value detector configured to detect a heating value of the fuel gas; a temperature detector attached on the gas feed pipe between the fuel gas heating/cooling device and the gas turbine unit configured to detect a temperature of the fuel gas; and a temperature control device of the fuel gas heating/cooling device configured to control temperature of the fuel gas supplied to the gas turbine power generation unit, characterized in that the LNG power plant further comprises a device for detecting a status of the LNG vaporization facility based on the number of open BOG outlet valves, wherein the temperature control device has: a target temperature calculator configured to receive a signal indicating the number of open boil off gas outlet valves, and, based on the signal, to calculate a target temperature of the fuel gas introduced to the gas turbine power generation unit, this signal being used as a state quantity signal equivalent to the heating value of the fuel gas; and a command generator connected to the target temperature calculator and the fuel gas heating/cooling device, the command generator being configured to receive the target temperature and a signal of temperature of the fuel gas detected by the temperature detector and generate a command to control the fuel gas heating/cooling device by comparing the target temperature and the temperature of the fuel gas. a gas turbine power generation unit having a gas turbine and a power generator; an LNG vaporization facility configured to feed vaporized LNG as a fuel gas to the gas turbine power generation unit, wherein the LNG vaporization facility has a plurality of LNG storage tanks, the LNG storage tanks are connected to a common boiled off gas, BOG, compressor through respective BOG outlet valves, the LNG storage tanks are connected to a common vaporizer through respective boost pumps; a gas feed pipe extending from the BOG compressor and the vaporiser of the LNG vaporization facility to the gas turbine power generation unit; a fuel gas heating/cooling device disposed between the LNG vaporization facility and the gas turbine unit on the gas feed pipe, configured to heat and cool the fuel gas introduced into the gas turbine power generation unit; a heating value detector configured to detect a heating value of the fuel gas; a temperature detector attached on the gas feed pipe between the fuel gas heating/cooling device and the gas turbine unit configured to detect a temperature of the fuel gas; and a temperature control device of the fuel gas heating/cooling device configured to control temperature of the fuel gas supplied to the gas turbine power generation unit, characterized in that the LNG power plant further comprises a device for detecting a status of the LNG vaporization facility based on the number of open BOG outlet valves, wherein the temperature control device has: a target temperature calculator configured to receive a signal indicating the number of open boil off gas outlet valves, and, based on the signal, to calculate a target temperature of the fuel gas introduced to the gas turbine power generation unit, this signal being used as a state quantity signal equivalent to the heating value of the fuel gas; and a command generator connected to the target temperature calculator and the fuel gas heating/cooling device, the command generator being configured to receive the target temperature and a signal of temperature of the fuel gas detected by the temperature detector and generate a command to control the fuel gas heating/cooling device by comparing the target temperature and the temperature of the fuel gas. a target temperature calculator configured to receive a signal indicating the number of open boil off gas outlet valves, and, based on the signal, to calculate a target temperature of the fuel gas introduced to the gas turbine power generation unit, this signal being used as a state quantity signal equivalent to the heating value of the fuel gas; and a command generator connected to the target temperature calculator and the fuel gas heating/cooling device, the command generator being configured to receive the target temperature and a signal of temperature of the fuel gas detected by the temperature detector and generate a command to control the fuel gas heating/cooling device by comparing the target temperature and the temperature of the fuel gas.