An air conditioning system comprises a first air duct having an inlet port and an exhaust port opening into a room, a room air circulating fan for introducing the air inside the room into the first air duct through the inlet port and discharging the air into the room through the exhaust port of the first air duct, solar heat collector for producing hot air by utilizing solar heat, a second air duct adjacent to the first air duct on the inlet port side thereof, hot air feeding fan for feeding the hot air from the solar heat collector into the second air duct, a rotary total heat exchanger for dehumidification disposed between said first and second air ducts so as to extend severally in the two ducts, a third air duct adjacent to the first air duct on the downstream side of the rotary total heat exchanger, outside air feeding fan for feeding the outside air into the third air duct, a stationary multi-diaphragm-type sensible heat exchanger for cooling disposed between the first and third air ducts so as to be located in common inside said two air ducts.