Patent ID: 8893979

Claim:
A thermostat device having a thermal expansion unit that expands with a temperature increase and contracts with a temperature decrease, the thermal expansion unit built into a case so as to be susceptible to effects of heat from outside the case, the thermostat device comprising: a piston disposed inside the case along an axial direction of the case and that advances and retreats with expansion and contraction of the thermal expansion unit, the piston having an inner end that is immersed in the thermal expansion unit and an outer end that protrudes from an opening in one end of the case; a guide member that is inserted into the case from the opening in one end of the case and slidably holds the piston; a seal member that is inserted into the case from the opening in one end of the case and holds the thermal expansion unit so that the thermal expansion unit does not leak from a chamber in which it is contained; and a first valve fitted onto the exterior of the case at one end of the case and that opens and closes a flowpath, wherein a portion of the case for fitting the first valve onto the exterior of the case, portions of the case for inserting the guide member, and a portion of the case for inserting the seal member are disposed so as to be offset from each other in an axial direction and in a diametrical direction of the case, and a diameter of a portion of the case that guides the first valve onto the case is configured to be smaller than an outer diameter of the case where the first valve is fitted onto the case, and inner diameters of the case where the guide member and the seal member are inserted into the case are configured to be smaller than the inner diameter of the case where first valve is fitted onto the case.