A rotation unit is supported to a device main body unit so as to rotate about a rotation supporting point. The rotation unit is rotated from a closure posture close to the device main body unit until a rotation limit position at 180 degrees. A magnet is fixed to the rotation unit at a position away from the rotation supporting point, and the device main body unit is provided with a detector capable of distinctly detect magnetic fields in two directions. When the rotation unit is rotated from the closure posture at a predetermined angle, a first open detection output is obtained form the detector and a display unit provided to the rotation unit is turned ON. The rotation unit is further rotated and when a second open detection output is obtained from the detector, the display content of the display unit is switched to be turned upside down.