A heat storage device of a vehicle may include an insulation container, a coolant passage connected to an engine, a heat exchanger having a fin formed on the coolant passage inside the insulation container, a phase change material charged in the insulation container to exchange heat with flowing coolant, a phase change material temperature sensor, a pressure sensor, an engine coolant temperature sensor, and a control portion that circulates the coolant according to the driving condition of the engine and the coolant temperature such that the coolant exchanges heat with the phase change material. Accordingly, fuel for warming an engine or heating an interior room is reduced, a separate heating device or a warm up device such as a PTC heater can be replaced, quality of the exhaust gas is quickly improved, and there is a merit in overcoming environmental regulations.