An air conditioner includes: a stepped portion 61 provided on a side of an outlet 5 of an air passage wall 6; an air passage extension 8 having a rotary shaft 82 in the outlet 5, the air passage extension 8 being rotatable in an opening direction about the rotary shaft 82 to bring a rear end 81 into abutment with the stepped portion 61 in such a manner that the air passage extension 8 integrates with the air passage wall 6 to form a curved surface of a predetermined curvature; and a rotary mechanism configured to cause the air passage extension 8 to rotate in such a manner as to bring the rear end 81 into abutment with the stepped portion 61 when the air conditioner is put into operation.