PURPOSE: To enable a small-sized display to be installed at a suitable position of an I/O section, by sequentially displaying error information with a display element for one digit's share with shifted time at each digit, in a processor provided with a plurality of I/O sections and its control section.

CONSTITUTION: In a processing device provided with a plurality of I/O sections 13 and its control section 10, a display section 15 consisting of a display element for only one digit's share is provided, and if any of the sections 13 has an error, error information consisting of a plurality of digits is sequentially displayed with the display section 15 consisting of the display element of one digit only with shifted time for each digit. Thus, the number of displays can be decreased and the display can be made small in size.