The controller includes a program storage that stores programs specifying a plurality of operations associated with at least one operable unit; a program executor that executes the programs; an operation executor that causes the operable unit to operate according to the programs; and an operable unit manager that manages control of the programs. When a program is called from one of the programs, the operable unit manager obtains control of a group associated with the operable unit and specified in the called program, and releases control of a group other than the group associated with the operable unit and specified in the called program.