PURPOSE: To make it possible, when a power failure occurs, to clearly display the occurrence of a power failure and its content with only a single display element by displaying the occurrence of power failure by flickering a LED differently in accordance with the content of the failure.

CONSTITUTION: CPU 51 of power supply controller 15, when detecting a power failure, initiates a timer in the controller 15, and carriers out the on/off control of LED 19. Further, when about two seconds pass, CPU 51 restarts the timer, and turns on LED 19 to inform the operator that reporting the error status starts. Next, the error status is represented with 4 bits, and when a bit indicates '1', it is lighting for long while '0' is lighting for short, and thus 4 bits light sequentially to display 15 types of power failures with a single LED 19. With this, the operator is informed clearly of the occurrence of a power failure and its content.