PURPOSE: To perform a defrosting mode operation of the air conditioner with excellent efficiency without giving the feeling of coldness to the user by carrying out the defrosting mode operation of the air conditioner in a state where the set temperature is raised to a value which is higher than the indoor temperature selected by the user, without stopping the operation of the compressor.

CONSTITUTION: A defrosting operation judging portion 17 allows the air conditioner to continue to operate as it is when a suction temperature Ta is lower than a set temperature T1 selected by the user. In a case where the former is higher than the latter, when the temperature Tb of an outdoor heat exchanger 3 is higher than the set temperature T4 of the outdoor heat exchanger, the defrosting operation judging portion 17 causes the compressor 1 to stop the operation, and starts the compressor 1 to operate when the suction temperature Ta reaches a set temperature T3. In a case where the former is lower than the latter, the defrosting operation judging portion 17 switches a four-way valve 2 and judges to carry out the defrosting operation.