A clothes treating apparatus includes a drum configured to accommodate therein an object to be dried, an air suction device configured to form a flow path of air introduced into the drum, an air exhaustion device configured to form a flow path of air exhausted from the drum, a condenser disposed to heat air sucked into the drum through the air suction device, an evaporator disposed to cool air exhausted from the drum the air exhaustion device, and a compressor and an expander configured to constitute a heat pump together with the condenser and the evaporator. The method includes a temperature detection step of detecting a temperature change of air passing through the condenser or the air suction device, and a determination step of determining that refrigerant leakage has occurred when a temperature decrease amount measured in the temperature detection step is more than a predetermined level.