Disclosed is an indoor unit for an air conditioner. The indoor unit for the air conditioner according to the present invention includes: a cabinet assembly forming an external appearance of the indoor unit and having an air suction port formed in a rear of the cabinet assembly; a filter module disposed at the air suction port to filter dust contained in air being introduced through the air suction port; a filter cleaner configured to move upward and downward in a rear of the filter module to remove foreign substances stuck in the filter module; a guide rail vertically disposed on one side of the filter module and configured to guide upward and downward movement of the filter cleaner, wherein the filter cleaner comprises: a mobile gear configured to rotate while engaged with the guide rail to move the filter cleaner upward and downward with respect to the filter module, a gear motor configured to rotate the mobile gear, an agitator configured to rotate in friction with the filter module, a dust container disposed downward of the agitator and collecting foreign substances separated from the filter module due to the rotation of the agitator, and a guide roller bringing the filter cleaner into close contact with the filter module so that part of the agitator rotates while in contact with the filter module.