To prevent excessive sensitivity of a sensor for opening and closing a valve by forming a ventilation port inside a valve, arranging a heat insulative member on an air layer outside thereof, and sensing room temperature.

A heat insulative member 11 is arranged in an air layer A. A temperature sensing opening/closing valve 1 is arranged on an upper ventilating port 16, while a ventilating V cap is arranged on a lower ventilating port 17. When room temperature is less than 8°C, a temperature memory spring 2 is in an extention state, a valve member 8 of the valve 1 is seated at a valve seat 9 for preventing underfloor air from entering the room. When the room temperature exceeds 8°C, the spring 2 is contracted. The valve member 8 is separated from the valve seat 9 against a returning spring 3, for communicating the underfloor with the room. When the room temperature exceeds 28°C, the spring 2 is further contracted. The valve member 8 is seated at a valve seat 10 for interrupting air communication. It is thus possible to freely circulate fluid within a range of a set temperature, and stop the fluid outside the range with a simple structure and a little maintenance.