PURPOSE: To effectively heat cooling water through heating means by interrupting communication between a radiator passage and a circulation passage at the time of warming-up state of an engine, interrupting the communication between the bypass passage and the circulation passage or throttling the communication sectional area.

CONSTITUTION: A temperature sensing valve device 10 is arranged on a connection part between a bypass passage 2 and a circulation passage and a radiator passage. At the time of warming-up state of an engine, that is, when a temperature of cooling water is a specified value or lower, main and bypass valves 18, 19 are at closed position, being abutted against respectively upper and lower valve seats 21, 22. Substantially only the side of a heater E is connected to the side of a water pump P. The cooling water is circulated only through the circulation passage, for effectively drawing out performance of the heater E. In such a state, the bypass passage 2 is connected to the side of connection ports 13, 14 through a second communication port 24, that is, to the side of the circulation passage. A flow rate of the cooling water is set considering a limit of an engine inner pressure. The bypass passage 2 may not be provided in some cases, accordingly.