Provided is a thermostat device capable of reducing flow resistance due to a thermal-operating unit and a frame support and also reducing the pressure loss in the flow passage. The thermostat device is provided with a control valve which opens and closes a flow passage in a housing based on expansion or contraction of a thermal expansion body in a thermo-sensitive element and a spring that biases the control valve to close and a spring receiving frame that receives one end of the spring. A thermal-operating unit is incorporated into the housing by locking the spring receiving frame to the frame supports formed in the flow passage of the housing. At the upstream side of the coolant flow at the frame support, a rectifier is disposed that prevents water streams from colliding by detouring the flow passage of the coolant heading to the frame support and the spring receiving frame.