To reduce an operating force and prevent unstable operating force by generating in a motor a driving force which is increased considering amount of change preset based on a difference between the operation force and threshold value upon determination that the operating force has exceeded a threshold value.

When an operating force is increasing even if an operating force detecting signal Fin is less than a threshold value Fsl, it means that a running load is increasing. In this case, if amount of change dFa becomes a negative and a drive force is reduced, an operation force is increased to a large extent as the reaction and the operation force becomes unstable. Therefore, the operation force is stabilized by setting amount of change dFa to zero to maintain the preceding value. During increase of operation force, when the operation force detecting signal Fin becomes larger than the threshold value Fsl even if it does not reach the setting value Fs, a positive amount of change dFa is given to quickly raise the drive force to prevent that the operation force becomes large unnecessarily.