To provide an air conditioning device inhibiting deterioration of heating capacity due to frost formation on an outdoor heat exchanger and inhibiting increase in noise.

In the air conditioning device 1, when a difference between outdoor temperature To and the temperature Te of the outdoor heat exchanger increases, a determination part 43 of a control section 4 determines that frost formation on the outdoor heat exchanger 13 is increased, and performs operation control for when frost is forming, which decreases the rotation speed of an outdoor fan 23. At this time, the operating frequency of a compressor 11 is increased in accordance with the amount by which the temperature of an indoor heat exchanger 15 is decreased. In the control section 4, there are preset a change amount for each step by which the operating frequency of the compressor 11 is changed stepwise. Each time the temperature of the indoor heat exchanger 15 decreases by a predetermined amount, the control section 4 increases the operating frequency of the compressor 11 by the change amount for raising it to the next upper step from the present step and decreases the rotation speed of the outdoor fan 23 according to the change amount.