Abstract: By opening and closing the sub display with respect to the main display D1 via a hinge H mounted on the side portion, a variety of uses, such as to display different information on the two different displays, are easily realized, whereby easily supporting diversification of displayed information expected in the future and improvement of the functions. The sub display can be rotated upside down in addition to the horizontal open/close movement with respect to the main display D1, thereby increasing the possible states of use. When the sub display is rotated upside down by 180°, each button B and the markings marked thereon rotates and inverted as well, the marking is shown in the normal orientation, but not inverted orientation as a consequent, thereby facilitating identification and operation of each button. The state of currently selected/connected source is displayed on one of the main display D1 and the sub display.