To prevent the non-coincidence of definition data by updating the definition data of an engineering device only when data read from a process controller coincide with the tentatively held changed definition data.

The difinition data down-loaded from the engineering device 1 to the process controller 3 are gathered in the buffer 4 of the engineering device 1 in a constant cycle and displayed on a change screen 2. Then, when the difinition data are changed on the change screen 2, while the data are tentatively stored in the buffer 5, they are transferred to the process controller 3, stored in a memory and transferred from the process controller 3 to the butter 4 of the engineering device 1. A data comparison part 6 compares the changed data tentatively stored in the butter 5 with the changed data stored in the buffer 4, and only when both coincide, transfers the changed data to a storage device 7 inside the engineering device 1 and updates the data.