When change amount information calculated by a change amount information calculating unit satisfies a start condition and a signal condition is true for an operation instruction the start condition and the signal condition of which are defined, an operation instruction execution control unit determines a start of the corresponding operation instruction and determines operation completion based on a completion condition determined in advance of the operation instruction. An operation instruction executing unit executes the operation instruction the start of which is determined by the operation instruction execution control unit and stops the operation instruction when the operation completion is determined by the operation instruction execution control unit.