PURPOSE: To simplify constitution, by providing a release adjusting valve whose one end is connected with a gaseous phase of a pressure chamber and the other end is connected with the atmosphere is opened and closed under the maximum and minimum states of a pressure chamber.

CONSTITUTION: Gauge pressures of a first pressure chamber 8 and a second pressure chamber 9 are made into 0kg/cm2G. When high temperature exhaust gas is started to flow, calorific value of the high temperature exhaust gas is transmitted to a gaseous phase 11 through a pipe wall of a liquid pipe 4, the gaseous phase 11 is expanded thermally and pressure of the gaseous phase of the first pressure chamber is increased gradually. When the gaseous phase of the first pressure chamber 8 exceeds 0.1kg/cm2G, water in the first pressure chamber 8 rises in a transport pipe 5 and starts to move to the second pressure chamber 9. When the gaseous phase pressure of the first pressure chamber 8 becomes 0.5kg/ cm2G, a release adjusting valve 6 becomes open, the first pressure chamber 8 and the atmosphere are connected with each other and the pressure of the first pressure chamber begins to fall. When the pressure of the first pressure chamber becomes 0.1kg/cm2G, the release adjusting valve 6 becomes closed.