PURPOSE: To remove the thermal effect by the cooling water temperature to a mechanical seal and prevent the leak of the cooling water from the mechanical seal.

CONSTITUTION: Temperature detectors 21, 22 are provided on the first-stage seal chamber 3a and the second-stage seal chamber 3b respectively. Temperature regulating valves 34, 36 are provided on the downstream side of the first-stage seal chamber 3a and the second-stage seal chamber 3b. Temperature signals of the temperature detectors 21, 22 are fed to the temperature regulating valves 34, 36 to regulate the temperature of the cooling water. The temperature- regulated cooling water passes a cooling water return pipe 26, a water feed pump 27 and a heat exchanger 28 from an outlet valve 25 connected to the outflow side of the regulating valves 34, 36, and flows into the first-stage seal chamber 3a and the second-stage seal chamber 3b from inflow pipes 31, 32 respectively.