PURPOSE: To prevent a room temperature from becoming much lower than a set value at the time of completion of a defrosting operation to remove frost on an outdoor heat exchanger during heating operation of an air conditioner.

CONSTITUTION: For each defrosting operation of an air conditioner, the defrosting operation condition data is stored, and a defrosting start time is predicted by this defrosting operation condition data, and a set value for a room temperature is set higher by a specified value α before the predicted time by a specified period of time to make the room temperature higher than a set value Ts at the time of defrosting operation so that the room temperature does not become much lower than the set value Ts at the end of a defrosting operation.