A refrigerator including a compressor, a condenser, and an expansion unit that constitute a refrigeration cycle, the refrigerator comprising: 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 transmitting unit configured to generate a sound of a first volume to the evaporator; and a sound receiving unit configured to receive a sound of a second volume formed after the sound transmitted by the sound 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, wherein the refrigerator further comprises: a sensor mounting portion provided to the inner case and on which the sound transmitting unit and the sound receiving unit are mounted; and a reflective plate configured to reflect the sound transmitted from the sound transmitting unit, the sensor mounting portion is disposed at a side of the evaporator, characterized in that: the reflective plate is disposed at an opposed side of the sensor mounting portion with respect to the evaporator. 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 transmitting unit configured to generate a sound of a first volume to the evaporator; and a sound receiving unit configured to receive a sound of a second volume formed after the sound transmitted by the sound transmitting unit reflects from or passes through the evaporator, and a sound transmitting unit configured to generate a sound of a first volume to the evaporator; and a sound receiving unit configured to receive a sound of a second volume formed after the sound transmitted by the sound 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, wherein the refrigerator further comprises: a sensor mounting portion provided to the inner case and on which the sound transmitting unit and the sound receiving unit are mounted; and a reflective plate configured to reflect the sound transmitted from the sound transmitting unit, the sensor mounting portion is disposed at a side of the evaporator, characterized in that: the reflective plate is disposed at an opposed side of the sensor mounting portion with respect to the evaporator.