A liquefied gas reliquefier reliquefies boil-off gas resulting from evaporation of liquefied gas in a liquefied-gas storage tank to prevent a rise in the internal pressure of the liquefied-gas storage tank. The liquefied gas reliquefier includes a cooling unit for liquefying a secondary refrigerant, a liquefied-secondary-refrigerant feeding unit for feeding the liquefied secondary refrigerant, and a heat exchange unit disposed in the secondary-refrigerant circulating channel to condense the BOG by heat exchange between the BOG and the liquefied secondary refrigerant. The heat exchange unit is disposed near the liquefied-gas storage tank. The cooling unit includes a plurality of pulse-tube refrigerators. The number of pulse-tube refrigerators in operation and/or the cooling capacities of the individual pulse-tube refrigerators are controlled based on a measurement result from at least one of a thermometer, a pressure gauge, and a pump discharge flow meter installed in the liquefied-gas storage tank.