To provide an apparatus and a method for preventing heating-medium leakage in a heater, in which a heating-medium leakage in an operation shutdown in restrained to a minimum, when heating-medium leakage is caused due to cracks, etc., existing in a circulation path.

Valves (thermally actuated valves 24, 26, 28, 30) are installed respectively at the inlets and the outlets of the heat-source equipment side in a circulation path (22), connecting the heat-source equipment (6) and space- seating terminals (2, 4); and the valve is closed at an operation shutdown time, and the circulation path between the heat-source equipment and the heater terminal is shut off to restrain heating-medium leakage to a minimum.