An indoor unit of an air-conditioning apparatus, the indoor unit comprising: a casing having a rear surface to be mounted to an indoor wall; a front panel serving as a front surface of the casing, the front panel having a lower end serving as a front end of a bottom surface of the casing; an air inlet provided in the casing; an air outlet that opens to the bottom surface; a heat exchanger and an air-sending device each arranged in an air passage extending from the air inlet to the air outlet; an up-down air-directing plate disposed and rotatably supported in the air outlet, the up-down air-directing plate covering the air outlet in an off state, the up-down air-directing plate being rotated and adjusted in angle to adjust a direction of air blown from the air outlet in an up-down direction in an on state; an auxiliary air-directing plate disposed along a longitudinal direction of the air outlet; and a rotating shaft about which the auxiliary air-directing plate rotates, the rotating shaft being disposed inside the air outlet and on a side of the front surface of the casing, the rotating shaft being positioned above the lower end of the front panel, the rotating shaft being spaced from a front wall that is a wall of a front surface side of the air outlet, the front wall being disposed on a side of a front surface of an air passage extending from the air-sending device to the air outlet, in the off state, the auxiliary air-directing plate being positioned inside the air outlet such that a free end of the auxiliary air-directing plate opposite from one end of the auxiliary air-directing plate fixed to the rotating shaft is positioned closer to the rear surface than is the rotating shaft, in the on state, the auxiliary air-directing plate being rotated in a direction from the rear surface to the front surface of the casing, and the free end being protruded from the air outlet to an outside of the casing such that the free end extends downward from the lower end of the front panel, in a cooling operation, the auxiliary air-directing plate being spaced from the front wall. a casing having a rear surface to be mounted to an indoor wall; a front panel serving as a front surface of the casing, the front panel having a lower end serving as a front end of a bottom surface of the casing; an air inlet provided in the casing; an air outlet that opens to the bottom surface; a heat exchanger and an air-sending device each arranged in an air passage extending from the air inlet to the air outlet; an up-down air-directing plate disposed and rotatably supported in the air outlet, the up-down air-directing plate covering the air outlet in an off state, the up-down air-directing plate being rotated and adjusted in angle to adjust a direction of air blown from the air outlet in an up-down direction in an on state; an auxiliary air-directing plate disposed along a longitudinal direction of the air outlet; and a rotating shaft about which the auxiliary air-directing plate rotates, the rotating shaft being disposed inside the air outlet and on a side of the front surface of the casing, the rotating shaft being positioned above the lower end of the front panel, the rotating shaft being spaced from a front wall that is a wall of a front surface side of the air outlet, the front wall being disposed on a side of a front surface of an air passage extending from the air-sending device to the air outlet, in the off state, the auxiliary air-directing plate being positioned inside the air outlet such that a free end of the auxiliary air-directing plate opposite from one end of the auxiliary air-directing plate fixed to the rotating shaft is positioned closer to the rear surface than is the rotating shaft, in the on state, the auxiliary air-directing plate being rotated in a direction from the rear surface to the front surface of the casing, and the free end being protruded from the air outlet to an outside of the casing such that the free end extends downward from the lower end of the front panel, in a cooling operation, the auxiliary air-directing plate being spaced from the front wall.