PURPOSE: To facilitate the maintenance of the software, improve the development efficiency of the software, shorten the development time, and improve the reliability of software.

CONSTITUTION: An input/output process program generation part 5 generates an input/output processing program 15 from hardware constitution data 11 of a hardware constitution input and storage part 1 and input/output signal data 13 of an input/output signal registration and storage part 3. A communication input/output program generation part 6 generates a communication input/ output processing program 16 from communication input/output information 12 and input/output signal data 13 of a communication input/output information input and storage part 2. A logic part program generation part 7 generates a logic part program 17 from the input/output signal data 13 and logic diagram data 14 of a logic input and storage part 4. A program merging part 8 generates a control program 19 by merging the input/output processing program 15, communication input/output processing program 16, logic part program 17, and a user program 18.