An air conditioner having an improved assembly structure of panels includes a lower panel located at a bottom surface thereof, an upper panel located at an upper surface thereof, front and rear panels located at front and rear surfaces thereof, and side panels to couple the front and rear panels. One side of each of the lower panel and at least one panel is provided with a protrusion and the other side thereof is provided with a coupling groove, so that the lower panel is coupled to at least one of the front panel and the side panels by coupling of the protrusion and the coupling groove. It may be possible to provide an air conditioner capable of reducing the number of fastening members coupled to respective panels and being free from restraint of an installation space.