To obtain a heat exchanger which continuously monitors turbidity degree of a cooling water.

A steam supply pipe 3 is connected to a jacket portion 2 through a control valve 7. A suction unit 6 is connected to a lower end of the jacket portion 2 through a steam trap 4 and an on-off valve 9. The suction unit 6 is composed of a fluid ejector 13, a cooling water tank 14 and a circulation pump 15. A strainer member 18 is mounted at an entrance side of the circulation pump 15, and a flow meter 22 is mounted to an exit side. A temperature sensor 20 is mounted to the cooling water tank 14. A clogging state of the strainer member 18 is detected based on a detected flow rate value of the flow meter 22, consequently turbidity degree of the cooling water in the cooling water tank 14 can be monitored indirectly and continuously.