When a plurality of electric devices is charged, each electric device is charged by priorities. The data processing apparatus related to the present invention comprises; a first data processing unit which comprises a first memory, a first data control section and a first battery; a second data processing unit which comprises a second memory, a second data control section and a second battery. The first data processing unit and the second data processing unit can be mechanically attached to and removed from each other. The data processing apparatus related to the present invention comprises; a data transfer control section which transfers data between the first memory and the second memory when the first data processing unit and the second data processing unit are mechanically connected with each other; and charge control sections which charge the first battery and the second battery when the first data processing unit and the second data processing unit are mechanically connected with each other, and the data processing apparatus is connected to the external power supply means.