PURPOSE: To shorten time for executing diagnosis at the information processor provided with plural sub units.

CONSTITUTION: Shift-out data provided from all sub units 21-24 are compared, when the compared result shows non-coincidence, this compared result is held, and an error signal is sent to an external diagnostic device so as to show the non-coincidence of shift-out data. Each time a shift clock is supplied, the number of supplied shift clocks is counted, and the count value in the case of receiving the error signal is held and supplied to the external diagnostic device. The expected value of shift-out data from the external diagnostic device is received, it is detected whether the shift-out data provided from all the sub units 21-24 are coincident with the expected value or not and when there is non-coincidence with the expected value, the sub unit outputting the non-coincident shift-out data is reported to the external diagnostic device as a fault sub unit.