An indoor unit for an air conditioner of which at least one portion of an exterior is defined by a panel exposed to the outside, the indoor unit comprising: a window insert (260, 263, 264, 265, 266) received in an installation hole defined in the panel; a receiving part (432, 435) disposed under the window insert (260, 263, 264, 265, 266) and being adapted to receive a manipulation signal passing through the window insert (260, 263, 264, 265, 266), the manipulation signal being generated by a remote controller that is manipulated by a user; and an LED (440, 441, 442, 443, 444) disposed on a side of the receiving part (432, 435) to emit light toward the window insert (260, 263, 264, 265, 266), thereby displaying an operation state of the indoor unit to the outside; wherein the window insert (260, 263, 264, 265, 266) is being formed of light translucent material so that the light emitted from the LED (440, 441, 442, 443, 444) is emitted to the outside, and the manipulation signal of the remote controller is received into the receiving part (432, 435), and characterized in that the indoor unit further comprises: an inspection hole defined in the panel; a cover opening/closing the inspection hole and defining a portion of an exterior of the panel, wherein the inspection hole and the cover are disposed on at least one of the four corners of the panel, and the cover comprising the installation hole and the window insert (260, 263, 264, 265, 266), and wherein the receiving part (432, 435) is disposed at a position that corresponds to the lateral center of the window insert (260, 263, 264, 265, 266), and wherein the LED (440, 441, 442, 443, 444) is disposed laterally outside the window insert (260, 263, 264, 265, 266) when view along the center axis of the insertion hole. a window insert (260, 263, 264, 265, 266) received in an installation hole defined in the panel; a receiving part (432, 435) disposed under the window insert (260, 263, 264, 265, 266) and being adapted to receive a manipulation signal passing through the window insert (260, 263, 264, 265, 266), the manipulation signal being generated by a remote controller that is manipulated by a user; and an LED (440, 441, 442, 443, 444) disposed on a side of the receiving part (432, 435) to emit light toward the window insert (260, 263, 264, 265, 266), thereby displaying an operation state of the indoor unit to the outside; wherein the window insert (260, 263, 264, 265, 266) is being formed of light translucent material so that the light emitted from the LED (440, 441, 442, 443, 444) is emitted to the outside, and the manipulation signal of the remote controller is received into the receiving part (432, 435), and characterized in that the indoor unit further comprises: an inspection hole defined in the panel; a cover opening/closing the inspection hole and defining a portion of an exterior of the panel, wherein the inspection hole and the cover are disposed on at least one of the four corners of the panel, and the cover comprising the installation hole and the window insert (260, 263, 264, 265, 266), and wherein the receiving part (432, 435) is disposed at a position that corresponds to the lateral center of the window insert (260, 263, 264, 265, 266), and wherein the LED (440, 441, 442, 443, 444) is disposed laterally outside the window insert (260, 263, 264, 265, 266) when view along the center axis of the insertion hole. an inspection hole defined in the panel; a cover opening/closing the inspection hole and defining a portion of an exterior of the panel, wherein the inspection hole and the cover are disposed on at least one of the four corners of the panel, and the cover comprising the installation hole and the window insert (260, 263, 264, 265, 266), and wherein the receiving part (432, 435) is disposed at a position that corresponds to the lateral center of the window insert (260, 263, 264, 265, 266), and wherein the LED (440, 441, 442, 443, 444) is disposed laterally outside the window insert (260, 263, 264, 265, 266) when view along the center axis of the insertion hole.