Disclosed is an indoor unit of an air conditioner, in which discharge units respectively provided on upper and lower portions of the indoor unit have an improved discharge structure such that the discharge units are interchangeable, to increase cooling efficiency regardless of installation position of the indoor unit. The indoor unit includes a cabinet; a first discharge unit being detachably provided on the cabinet and configured to discharge air in a forward direction; and a second discharge unit separated from the first discharge unit, being detachably provided on the cabinet and configured to discharge air in the oblique direction, the first discharge unit and the second discharge unit being interchangeable according to a height of a position at which the cabinet is installed. The indoor unit of the air conditioner sets the optimum direction of discharged air, thus increasing the cooling efficiency of an indoor space.