A defrost heat discharge system includes a drain duct configured to discharge heat from a defrost heater and to discharge condensed water that results from melting of frost on an evaporator by heat generated by the defrost heater, a drain pipe that connects a first space to a second space, that is configured to allow condensed water to flow from the first space to the second space, and that is configured to discharge heat generated by the defrost heater from the first space to the second space, a drain cap located at an end of the drain pipe and configured to open and close at least a portion of the drain pipe; and a condensing fan configured to receive heat from the defrost heater and discharge heat toward an outside of the second space based on the drain cap opening the portion of the drain pipe.