A tablet computer includes a mobile phone mounting portion which has determined width and length and is formed in the rear of the tablet computer in a recessed manner, guide grooves which are longitudinally formed on both lateral walls of the mounting portion, and a separation prevention member which is fixedly inserted into the guide grooves and has width and length corresponding to those of the mounting portion. The separation prevention member includes wing fixing portions which are fixedly inserted into the guide grooves of the lateral walls, determined width of wings which are extended upwards from the wing fixing portions and formed to bend toward the center of the mounting portion, respectively, and a determined width of cover which is provided in the range between one end of the separation prevention member and the wings.