An indoor unit for an air-conditioning apparatus, comprising: a casing having an air inlet formed in an upper surface of the casing and an air outlet formed below the air inlet; a fan_ and a heat exchanger provided inside the casing; at least one filter provided to the air inlet and configured to remove dust from air sucked into the casing by the fan; at least one cartridge provided to the air inlet so as to be freely mountable and dismountable, the at least one cartridge having a ventilation port formed in an upper surface of the at least one cartridge, a ventilation port formed in a lower surface of the cartridge, and a filter drive shaft configured to move the at least one filter, the at least one cartridge being configured to accommodate the at least one filter so that the at least one filter is freely mountable and dismountable; a filter drive motor configured to drive the filter drive shaft; a dust box comprising: a brush configured to clean the at least one filter; a brush drive shaft, to which the brush is mounted, the brush drive shaft being configured to rotate or swing the brush; and a dust collecting portion configured to collect the dust removed by the brush; and a brush drive motor configured to drive the brush drive shaft, the at least one cartridge having an opening port formed in one end portion of the at least one cartridge in a fore-and-aft direction and being configured to move the at least one filter in the fore-and-aft direction, the dust box being provided to be opposed to the opening port of the at least one cartridge so as to be freely mountable and dismountable and being configured to clean the at least one filter from the opening port by the brush. a casing having an air inlet formed in an upper surface of the casing and an air outlet formed below the air inlet; a fan_ and a heat exchanger provided inside the casing; at least one filter provided to the air inlet and configured to remove dust from air sucked into the casing by the fan; at least one cartridge provided to the air inlet so as to be freely mountable and dismountable, the at least one cartridge having a ventilation port formed in an upper surface of the at least one cartridge, a ventilation port formed in a lower surface of the cartridge, and a filter drive shaft configured to move the at least one filter, the at least one cartridge being configured to accommodate the at least one filter so that the at least one filter is freely mountable and dismountable; a filter drive motor configured to drive the filter drive shaft; a dust box comprising: a brush configured to clean the at least one filter; a brush drive shaft, to which the brush is mounted, the brush drive shaft being configured to rotate or swing the brush; and a dust collecting portion configured to collect the dust removed by the brush; and a brush configured to clean the at least one filter; a brush drive shaft, to which the brush is mounted, the brush drive shaft being configured to rotate or swing the brush; and a dust collecting portion configured to collect the dust removed by the brush; and a brush drive motor configured to drive the brush drive shaft, the at least one cartridge having an opening port formed in one end portion of the at least one cartridge in a fore-and-aft direction and being configured to move the at least one filter in the fore-and-aft direction, the dust box being provided to be opposed to the opening port of the at least one cartridge so as to be freely mountable and dismountable and being configured to clean the at least one filter from the opening port by the brush.