Disclosed therein is an air conditioner for a vehicle which includes a sealing member attached to one side of a door member of a mode door face-sealed with the inner face of an air-conditioning case by the inside wind pressure of the air-conditioning case so as to prevent vibration of the door member by wind pressure of the inside of the air-conditioning case and prevent air leakage from the face-sealed part, and which includes a rib formed on the door member for preventing excessive pressure of the sealing member in order to make actuating force of the door member uniform and to enhance a passenger's sense of manipulation.