PURPOSE: To attain quick and sure confirmation with simple constitution by checking whether or not an image before correction is a branch instruction every time the collation noncoincidence takes place in a microprogram image before and after correction to attain corresponding processing.

CONSTITUTION: When a central processing unit 2 starts its execution based on an image collation program stored in a main storage device 1, the image before and after the correction of microprogram is transferred to the device 1 from flexible disk devices 3, 4 respectively and the images are collated sequentially. At each noncoincidence, whether or not the image before correction is a branch instruction is checked and each image after the image before correction of a branched destination in case of a branch instruction and each image after correction caused with the noncoincidence and subject to collation restart based on a program storing noncoincidence information stored in the device 1 conditionally. On the other hand, in case of not a branch instruction, the information relating to the noncoincidence is reserved and the confirmation of source correction of the microprogram is confirmed quickly and surely by the automatic confirmation with simple constitution.