A clothes treating apparatus includes a drum, an air suction unit forming a flow path of air introduced into the drum, an air exhaustion unit forming a flow path of air exhausted from the drum, a condenser heating air sucked into the drum through the air suction unit, an evaporator cooling air exhausted from the drum through the air exhaustion unit, a compressor compressing refrigerant introduced from the evaporator, and a variable expander expanding a refrigerant introduced from the condenser, and having a variable open degree. An operation method includes measuring a temperature of a refrigerant into the evaporator, and a temperature of a refrigerant into the compressor, and decreasing an open degree of the variable expander when a temperature difference between the two measured temperatures is less than a predetermined first value.