A heat pump type air conditioner having an improved defrosting structure and a defrosting method for the same. When frost is not excessively accumulated on piping of an outdoor heat exchanger, a solenoid valve is controlled such that warm refrigerant from a compressor intermittently passes through a second pipe line, a heat discharging pipe line, and a third pipe line. When the air conditioner is operated in heating mode, the amount of frost accumulated on the outdoor heat exchanger is deduced from the temperature of the piping of the outdoor heat exchanger, and then a defrosting operation is performed based on the temperature of the piping of the outdoor heat exchanger. Consequently, the frost accumulated on the outdoor heat exchanger is quickly removed based on the amount of frost accumulated on the outdoor heat exchanger, and the period of time for which the air conditioner is not operated is reduced, whereby more comfortable and pleasant heating function is provided to a user.