THERMOSTAT DEVICE

A thermostat device is provided that smoothens the flow of the coolant to keep the pressure loss small and can sufficiently secure the flow rate of the coolant from the radiator side to the engine side. A housing having a first inlet for introducing a coolant cooled by a radiator and a coolant outlet supplied to the internal combustion engine, a thermo-element accommodated in the housing that moves axially depending on the temperature of the coolant, a control valve that controls the amount of coolant introduced from the first inlet as the thermoelement moves in the axial direction, and a slope having an upward slope from the outlet side to the valve seat side inside the exit-side conduit extending from the valve seat in the housing, wherein the control valve is in contact with in the valve-closed state, toward the flow outlet of the coolant, are provided.