To permit the perfect defrosting of an outdoor heat exchanger even when previous defrosting operation is finished forcibly not depending on the increase of a heat exchanger temperature.

When defrosting operation is finished forcibly, not depending on the increase of a heat exchanging temperature but depending on the elapse of interval of defrosting, the defrosting operation of next time is carried out forcibly even when the detecting values of a heat exchanger temperature sensor 13 and an outdoor air temperature sensor 14 are at outside of starting range of defrosting operation. The defrosting operation is repeated forcibly until the previous defrosting operation is finished depending on the increase of heat exchanging temperature. Even when a temperature detected by the heat exchanger temperature sensor 13 is increased under the insufficient defrosting condition of an outdoor heat exchanger 5, the defrosting operation is carried out to defrost the outdoor heat exchanger 5 without remaining any non-molten frost, whereby the freezing of the outdoor heat exchanger 5 is defrosted perfectly.