Abstract: An indoor unit for an air conditioner includes: a blower fan that is arranged in a casing; a heat exchanger that encompasses all air flow directions from the blower fan; a drain pan that is arranged below the heat exchanger; and an antimicrobial unit that is installed on the drain pan and has an antimicrobial agent to sterilize drain water. At least a part of the antimicrobial unit is arranged directly below the heat exchanger. The indoor unit has the antimicrobial agent arranged on the drain pan while a cross-sectional area of an outlet passage is prevented from being reduced.