PURPOSE: To execute normally the job at all times by providing a flip-flop storing temporarily the command of power supply keeping from a computer A and its driver and a relay so as to keep the supply of power even when the power switch of a computer B is turned off.

CONSTITUTION: The flip-flop (FF)1 set when a host computer (hereinafter H-CPU) uses a terminal computer (hereinafter T-CPU) and reset when the H-CPU does not use, a driver 2 obtaining a relay drive signal based on the set output signal and a relay 3 are provided, and this contact is connected in parallel with a power switch 4. When the user using the T-CPU turns on the power switch 4, the job is executed and the H-CPU uses the T-CPU so as to execute the job. Even when the power switch 4 is turned off, the FF1 is set by using an access signal from the H-CPU, the relay 3 is switched on and the job is executed similarly.