THERMOSTAT VALVE

[Problem] To provide a thermostat valve in which the amount of water leakage while the valve is closed is reduced to an infinitesimally small level and which is configured using a resin molding process to make the entire thermostat valve compact and lightweight and to reduce the number of parts. [Solution] A thermostat valve is provided with: a body housing (12) having an annular body section and a frame section which is provided to the other end surface side of the body section with legs therebetween, the body housing (12) being molded in one piece having a circular cylindrical shape from a synthetic resin material; a disk-shaped valve body (20) disposed on one end surface side of the body housing (12) so as to be capable of moving forward and backward in the axial direction; a spring receiver (24) for holding the end of a pressing spring means (22) away from the valve body and engaged with and held by the front end hook of an engagement arm (30) extended from the body housing; and a thermo-element (40) held by and affixed to an element guide (12c) provided on the frame section of the body housing, the thermo-element (40) operating the valve body in the valve opening direction according to fluid temperature. An annular stepped section having a top section with a predetermined width is provided at a portion of said end surface of the body housing, the portion being located close to an opening peripheral edge section, the annular stepped section serving as a valve seat section (16).