An electronic thermostat apparatus for controlling a temperature of a coolant of an engine in a vehicle may include a housing connected to a plurality of flow paths through which the coolant of the engine flows, a wax case installed inside the housing and provided with a wax accommodation space therein, a glow plug heater inserted in a wax filled inside the wax accommodation space and configured to generate heat by receiving an external power, a driving body engaged to the wax case and moving according to deformation of the wax by the heat of the glow plug heater, a main valve engaged to the driving body and configured to open/close a radiator-side flow path by a movement of the driving body, and an elastic member elastically biasing the main valve to the radiator-side flow path.