PURPOSE: To display a program after correction without parting a serial flow by deleting branch instructions and outputting the program in form wherein a corrected part of the main program is replaced with a correcting program.

CONSTITUTION: When data in execution form which are stored in a 1st data storage part 33 are corrected, the address (correction address) of the data to be corrected and correcting data represented in symbol form are inputted from an input device 1. A 1st registration part 24 checks whether or not the data in the symbol form are a branch instruction, converts the data into data in execution form when the data are not the branch instruction, and substitutes them for the data in the address of the corrected place in the data stored in the 1st data storage part 33. When the data are the branch instruction, on the other hand, the address of a branch instruction from a part other than the correction area to the correction area and the address of a branch instruction from the correction area to a part other than the correction area are registered in a correction address storage part 32, and the data in symbol form are converted into data in execution form to substitute for the data in the address of the corrected place.