When a portable information terminal device is connected with a cradle, a power interface is connected to a power interface being connected to an external power source so as to allow power to transfer. When the portable information terminal device is connected with the cradle, an optical interface is connected to an optical interface being connected to an external device so as to allow communications. A main function block having a control function to function when the portable information terminal device is not connected with the cradle, is connected to a main power source and the power interface so as to allow power to transfer. The optical interface is arranged so that power is supplied from only the power interface. In such arrangement, a terminal becomes more durable, because optical communication is performed. Further, only the external power source supplies power to the optical interface when the optical interface is connected with the cradle.