PURPOSE: To prevent important data from being lost and destroyed and to relieve an operator from anxiety by powering on a processor by a subswitch regardless of the state of a main switch when a control command is transferred from the processor to a terminal equipment.

CONSTITUTION: When a CPU6 generates a command for specifying an external reader 2 or an oiler 3, the command is detected by a detector 17 to set an FF18. Then, the driving means 21 of a solenoid 20 operates to close the subswitch 19 automatically. This subswitch 19 is provided in parallel to the main switch 22 and therefore, even when an operator performs wrong key operation to put the main switch 22 in operation, the main frame processor 1 is powered on by a power source 23 continuously, so that the terminal side also operates continuously. Thus, important data is neither lost nor destroyed and the operator need not pay special attention to the power supply switches, so the operator is relieved from anxiety.