An indoor unit and an air conditioning system using the same include a first communication module to communicate with a wired remote controller, a power switch connected to a power terminal of one or the other side of the first communication module, a ground switch connected to a ground terminal of one or the other side of the first communication module to constitute a pair with the power switch, and an indoor unit controller to turn on the power switch and the ground switch when an indoor unit supplies power to the wired remote controller, and to turn off the power switch and the ground switch when another indoor unit supplies power to the wired remote controller.