a binary power generation device is equipped with the flow path of a medium circulating through a heat exchanger , a turbine , a condenser , and a pump . a method for removing air that has intruded into the flow path of the medium includes : an air intrusion detection step of calculating , based on the pressure and temperature of a gas retaining portion communicatively connected to the flow path of the medium , a pressure threshold value obtained by adding the saturated vapor pressure of the medium and a margin value and of detecting , by comparing the pressure of a gas phase portion with the pressure threshold value , that air has intruded into the medium ; a medium liquefaction step of producing a gas by pressurizing a mixed gas of the medium and air to reduce the amount of the medium in the mixed gas ; and an exhaust step of exhausting the gas .