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