An air conditioner has: an air-conditioning case including an air passage; a plate-shaped door body that rotates about a rotation shaft; and an opposing wall provided in the air passage to define a gap between a tip portion of the door body and the opposing wall. A length of the opposing wall in a circumferential direction of the rotation shaft is larger than a thickness dimension of the tip portion of the door body. The opposing wall includes a first door facing surface and a second door facing surface. The air-conditioning case has a connecting surface connecting the first door facing surface and the second door facing surface. The second door facing surface is located outward with respect to the rotation shaft in a radial direction than the first door facing surface is.