PURPOSE: To make it possible to know the progress state of IPL(initial program load) operation by changing display contents in accordance with the progress state of the IPL operation.

CONSTITUTION: CPU(central processor) 1 is provided with ROM(read-only memory) 2 stored with control codes and special codes and address register 3. Special codes are read out of ROM2 in IPL operation in accordance with the progress of a RAM(random access memory) test, and address data are loaded into address register 3. By the data, the address of refresh memory 4 is assigned. Data written in refresh memory 4 are sent to character generator 5 and then converted into a bit pattern, which is displayed on display unit 6.