The invention provides a pressure control apparatus (100), which controls the pressure of a medium circulated in circulation paths (11, 12 and 16), wherein the circulation paths (11, 12 and 16) are arranged among the suction side and the discharge side of a pump (31) and respective prescribed objects thereof. The pressure control apparatus (100) comprises: a temperature detection part (71) for detecting the temperature of a medium in a circulation path (11); a pressure calculation part (52) for calculating the saturated steam pressure of the medium in the circulation path (11) based on the temperature measured by the temperature detection part (71); and a pressure control part (50) for controlling the pressure of the medium on the suction side of the pump so as to achieve the pressure of more than the saturated steam pressure calculated by the pressure calculation part (52). With the pressure control apparatus of the present invention, the pressure of the medium circulated in the circulation path can be controlled at the optimal pressure.