A control method of a washing machine is provided to accurately decide a time point for finishing a drying step and to thereby improve customer satisfaction about the drying function by preventing the drying step from being finished not after completely drying the laundry or unnecessary electricity consumption due to excessively long drying time. A control method of a washing machine comprises the steps for extracting moisture in hot air by cooling the heated air discharged/circulated from a rotary tub in a drying step through coolant, and discharging to the outside; periodically obtaining at least one change of temperature about the coolant used in the previous step and the extracted water(508); gradually increasing count values over a standard range every time the temperature change is over a preset standard range(512); and finishing the drying step if the count value is over the preset standard range.
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