The refrigerator comprises a compressor, a condenser, and an expansion unit that constitute a refrigeration cycle. The refrigerator further comprises a main body in which a storage chamber is formed, the main body including an inner case; an evaporator including a refrigerant pipe and cooling fins, the evaporator being configured to evaporate refrigerant that has passed through the expansion unit; a heating unit configured to provide heat for defrosting the evaporator; a frost sensor unit that is provided at one side of the evaporator configured to sense the amount of frost on the evaporator, the frost sensor unit including a sound-source transmitting unit configured to generate a sound-source of a first volume to the evaporator; and a sound-source receiving unit configured to receive a sound-source of a second volume formed after the sound-source transmitted by the sound-source transmitting unit reflects from or passes through the evaporator, and a control unit configured to control the heating unit to generate heat, when the difference between the first volume and the second volume reaches a predetermined value.