An indoor unit of an air conditioner includes a casing (1) defining a receiving cavity (10), a heat exchanger (2) and a fan (3) disposed in the receiving cavity (10) respectively, and a panel (4) disposed on a bottom of the casing (1). The panel (4) is movable between a close position in which both an air inlet (11) and an air outlet (12) of the receiving cavity (10) are closed and an open position in which both the air inlet (11) and the air outlet (12) are open. In the open position, the panel (4) at least partially separates the air entering via the air inlet (11) from the air exiting via the air outlet (12).