To provide an air conditioner capable of high efficient ventilation at a low cost without increasing the size of the whole of the air conditioner.

A cross flow fan 2 and a propeller fan 4 are mounted on rotary shafts 3a and 3b on both sides of a motor 3. A slit 5 is formed in a surface on the indoor machine body side opposed to the propeller fan 4, and an air exhaust port 7 opened and closed by an on-off plate 8 is formed in the back of the air conditioner body. During an air conditioning mode, an air conditioning part is driven, the on-off plate 8 closes the air exhaust port 7. During a ventilation mode, operation of the air conditioning part is stopped, and the on-off plate 8 opens the air exhaust port 7.