To provide an air conditioner that carries out a heating operation and also a defrost operation, thereby enhancing comfort.

The air conditioner includes a compressor 21 which operates the refrigeration cycle, an indoor heat exchanger 13 which exchanges heat with indoor air, and an outdoor heat exchanger 23 which exchanges heat with outdoor air. The air conditioner performs heating operation by driving the compressor 21, the heating operation being performed while the indoor heat exchanger 13 serves as the high temperature part of the refrigeration cycle and the outdoor heat exchanger 23 serves as the low temperature part of the refrigeration cycle. The air conditioner also performs defrosting operation for defrosting the outdoor heat exchanger 23 which serves as the high temperature part of the refrigeration cycle, the defrosting operation being performed while the refrigerant is caused to flow in the direction opposite the direction of the flow of the refrigerant in the heating operation. In the outdoor heat exchanger 23, a large number of fins 30 are affixed to refrigerant pipes 2 so as to be close to each other. Air flow passes through between the fins 30 to perform heat exchange. A water introduction section 31, 32 for closing each of the gaps between the fins 30 at one end thereof in the air flow path direction is provided at the lower end of the outdoor heat exchanger 23.