PURPOSE: To restrain the influence at the fault time and the inspection time within a minimum range, by providing independent power sources for respective plural devices and by providing plural power sources for respective important devices, in the data processing device having plural devices in the common unit.

CONSTITUTION: The first and the second switching devices 4 and 5 and control device 3 are mounted on unit 10, and power is supplied to devices 4 and 5 by power supply parts 11 and 12 having change-over switches SW1 and SW2, and power is supplied to device 3 by two power supply parts 13 and 14 having SW3 and SW4. Normally, SW1WSW4 are closed; and if a fault occurs in, for example, device 5 under this state, SW2 is opened to replace device 5, and thus, the data processing device continues the operation as it is without the influence upon operations of devices 4 and 3. Eveb if power supply part 13 is faulty, the fault is detected by the detecting means, and power is supplied from power supply part 14 to device 3, and thus, the data processing part continues the operation without stop.