An operation noise control method for an air conditioner includes: a step (S1) of detecting an operation mode of the air conditioner; a step (S2) of operating an air flow guide panel (20) in accordance with the detected operation mode and controlling the air flow guide panel (20) so as to form a duct-like outlet passage (10) in a vicinity of an outlet (5); a step (S3) of selecting a sound wave which is preset in accordance with the operation mode; and a step (S4) of radiating the selected sound wave in the duct-like outlet passage (10) from a speaker (21).