This paper suggests a new type interface using the user’s mouth open/close motions. The user’s face was observed by the USB camera and the changes in the darkness on the mouth image were utilized as an interface. In order to improve the procedure speed, the only image around the mouth was used for image processing. This focused image area could be moved according to the movement of the user’s face, based on the displacement of the nostril with respect to the original position. Moreover, the developed interface was applied to the operations of the meal support manipulator. In the test operation, the developed interface could be successfully used after a few times practices.