A program modification support device supports modifications of programs realizing functions of a process control system comprising a first process control device and a second process control device. The program modification support device includes a selector configured to select, from data used in a first program among the programs, data required to be maintained for continuing a first function when switching from the first process control device to the second process control device is performed, the first program being for realizing the first function required to be continued when the switching is performed.

A first process control apparatus in a process control system executes a non-update target program which is not an update target and an update target program which may be the update target, pauses the non-update target program based on a pause request from an outside, and transfers a context of the non-update target program to a second process control apparatus. The second process control apparatus in the process control system executes the non-update target program which is not the update target and an update target program after update, restores a context of the non-update target program by using the transferred context, initializes a context of the update target program, and causes the second program execution unit to resume the non-update target program and the update target program, based on a resuming request from the outside.

A first process control apparatus in a process control system executes a non-update target program which is not an update target and an update target program which may be the update target, pauses the non-update target program based on a pause request from an outside, and transfers a context of the non-update target program to a second process control apparatus. The second process control apparatus in the process control system executes the non-update target program which is not the update target and an update target program after update, restores a context of the non-update target program by using the transferred context, initializes a context of the update target program, and causes the second program execution unit to resume the non-update target program and the update target program, based on a resuming request from the outside.