Abstract: An air conditioner is installed in the respective floors of a building and has a housing built in a space between the ceiling of one story and the floor of another story lying above the story. The housing is provided with a first suction port and a first ejection port which communicate with the upper story through the floor, and a second suction port and a second ejection port which communicate with the lower story through the ceiling. A condensation heat exchanger and an evaporation heat exchanger are arranged in the housing. A first blower is arranged in the housing to conduct the air of the upper story into the housing through the first suction port and discharge the air into the upper story through the heat exchanger and first ejection port. A second blower is arranged in the housing to conduct the air of the lower story into the housing through the second suction port and discharge the air into the lower story through the heat exchanger and second ejection port.