[PROBLEMS] To improve user's convenience by cordoning off both of a screen for input and that for output, of which size and resolution is sufficiently large, in mobile information processing apparatus comprising a touch panel device. This is achieved only by additionally providing an interface device between the external unit and further additionally providing some functions to a signal processing and control device originally belonging to the mobile information processing apparatus.[MEANS FOR SOLVING PROBLEMS] Mobile information processing apparatus comprising a touch panel device; wherein an interface device is provided which sends an external display signal to the external unit equipped with a display device; and wherein a signal processing and control device can select control mode 1, in which it generates one digital display signal, and sends it to a touch panel device, and control mode 2, in which it generates two digital display signals and sends one to a touch panel device, and the other to an external output interface device.