PURPOSE: To contrive to transfer heat to a predetermined direction only in a heat pipe, by providing a part to displace a valve, made of shape memory alloy, at one end of a heat pipe, and by opening and closing the valve provided in a flow path of an operating fluid by the action of a part to displace the valve.

CONSTITUTION: When the inside of an exhaust pipe is sufficiently heated, the temperature in the heat receiving end 1A of a heat pipe 1 is higher than the heat radiating end 1C. At that time, a coil spring 3 made of shape memory alloy is in the stretched state, and a valve 5 is pulled by a spring 7 toward the side of a heat radiating end 1C, so that an operating fluid can feeely be circulated through the heat pipe 1. When an engine is stopped and the temperature in the exhaust pipe goes down below the predetermined temperature, the coil spring 3 made of shape memory alloy is contracted, and the valve 5 is pulled to the side of a heat receiving end 1A. The tapered part 5a of a valve comes in close contact with the tapered part 6a of a projection 6 which is to be a valve seat in the pipe. In such a manner, radiation of heat from the heat radiating end 1C is stopped.