To provide an outdoor unit of an air conditioner, capable of driving a desired fan even when wiring to a fan motor for making a plurality of installed fans turn around is wrong.

The outdoor unit 1 includes: an upper fan motor 21a and a lower fan motor 21b; an upper fan 20a and a lower fan 20b connected to these motors; a heat exchanger 30; an outside air temperature sensor 40; and a control means 100 having a CPU 110. The CPU 110 executes a connection determination mode when an outside air temperature detected by the outside air temperature sensor 40 is kept at a predetermined value or higher continuously for a predetermined time during rotation of only the upper fan 20a located near the outside air temperature sensor 40. When the result of the determination shows that wiring to each fan motor is wrong, control to each fan motor is replaced.