The invention provides an indoor unit of an air conditioner, the indoor unit can prevent temperature in electric member box from going up, and can realize suffocation fire extinguishment and extension burning under a condition in which a printed circuit board is on fire. The indoor unit of the air conditioner is provided with an electric equipment unit and a heat exchanger, the electric equipment unit is provided with the printed circuit board having the electric member and the electric member box for containing the printed circuit board, the electric equipment unit is configured on an upper side of a front surface of the heat exchanger, the electric member box has an outer side formed by a metal cover and a base substrate and an inner side formed by a flame-retarded resin housing, and the flame-retarded resin housing keeps and encircles the printed circuit board.