THERMOSTAT DEVICE

Provided is a thermostat device which improves the assembling work, reduces the manufacturing cost, and transfers heat to a temperature sensing/operating part more efficiently. The thermostat device includes a cylindrical high-temperature-coolant rectification part which forms a high-temperature coolant passage to bypass a high-temperature coolant heated by an engine, and is communicated and extended so as to partially or entirely cover the temperature sensing/operating part, permitting the high-temperature coolant flowing in the high-temperature coolant passage flow out from a discharge opening after being in contact with the periphery (bottom surface/side surface) of the temperature sensing/operating part, a receiving part provided on the outer periphery side of the high-temperature-coolant rectification part, a spring fitted between the valve body and the receiving part to press the valve body in a valve closing direction and press the receiving part in a direction away from the valve body, and a frame which is continual from an upper end of a piston shaft and engages with the pressed receiving part while receiving urging force thereof.