To set the operating frequency of the main body of equipment from external communication equipment.

The pulse signal of a fixed width is inputted from external communication equipment 11 for communicating with a main body 1 of equipment, this pulse width is counted by a timer to operate at the operating frequency of the main body 1 of equipment as a reference and by calculating the operating frequency of the main body 1 of equipment, communication baud rate setting is performed corresponding to the operating frequency. Since the baud rate is set by a program for debug/inspection stored in a built-in ROM 7, when the operating frequency of the main body 1 of equipment is not known, by calculating the operating frequency as mentioned above, the common built-in ROM can deal with plural operating frequencies. By preserving the calculated operating frequency of the main body 1 of equipment in a volatile memory 9 or non-volatile memory 10, an operating program stored in an external ROM 3 can be run corresponding to the operating frequency.