PURPOSE: To prevent misevaluation with an information processor by performing the write/read of data to a memory part in response to a read/write mode, and recording the executed microprogram steps to reinforce a test program.

CONSTITUTION: The microprogram steps are read out of a control memory part 2 and executed. While the microprogram addresses to be executed thereafter are set successively to an address register 1. In such a case, the output of the register 1 is supplied to a history memory part 5 and therefore '1', i.e., the contents of a write data holding means 6 is written to the address position of the part 5 corresponding to the executed microprogram address. Finally an indication is given to a maintenance diagnosis control part 9 to read the part 5 after setting an information processor in a maintenance diagnosis state. Thus the part 9 sets 0 to a mode indication means 8 and holds a read mode. Then a read address is set to the register 1 and the read contents are read out of a data holding means 7. Then the next address processing is carried out.