To achieve sufficient silencing effect in a wall-installation type air conditioner.

This method includes a step S1 for detecting an operation mode of the air conditioner, a step S2 for operating a wind guide panel 20 according to the detected operation mode and controlling the same to form a duct-like discharge path 10 near a discharge opening 5, a step S3 for selecting predetermined sound wave according to the operation mode, and a step S4 for radiating the selected sound wave to the duct-like discharge path 10 from a speaker 21.