PURPOSE: To correct a control program easily by setting an area for storing an entry table and a corrected program request in a program control device.

CONSTITUTION: When control is to be transferred to respective elements in an ROM2 in a program control I/O terminal device, the control is transferred in accordance with an entry table in a read/write memory R/W3. When it is necessary to correct the program request, the I/O terminal device stores a program request generated by correcting said program request in a control program storage area of the R/W3 and changes an entry address storage area for the program request to an entry address for the generated program request to attain the correction of the control program.