Mixing section for outdoor air and return air in an air-conditioning apparatus, the mixing section (21) being positioned between a supply duct (1) supplying outdoor air into a room (4) and a return duct (3) removing exhaust air from the room for mixing outdoor air (A) and return air (C). The supply and return ducts comprise adjusting devices (9, 20) for adjusting the air flows. To control the air flows at different mixing ratios and to make the mixing more efficient, guides (22, 25) are provided after the adjusting devices of both the supply device (1) and the return device (3) in a mixing space so as to divide the air flows passing through the adjusting devices into a plurality of separate interlapping air jets (A', C') crossing each other.