PURPOSE: A heating device of a seawater ballast tank is provided to reduce the steam necessary for heating a heavy oil storage tank by supplying the waste heat of a cooling system to a seawater ballast tank that is adjacent to the heavy oil storage tank. CONSTITUTION: A heating device of a seawater ballast tank comprises a seawater ballast tank(6), a seawater heat exchanger(2), and a temperature sensor(4). The seawater ballast tank is adjacent to a heavy oil storage tank(5) and stores seawater for stable sailing of a ship. The seawater heat exchanger supplies heated water to the seawater ballast tank. The temperature sensor senses the temperature of the seawater ballast tank.
