To suppress repetitive fluctuation of a driving force transmission characteristic caused by duty control of a current flowing to an electromagnetic coil in a driving force transmission controller controlling driving force by controlling duty of an electromagnet.

In this driving force transmission controller controlling the driving force by controlling the duty of the electromagnet, since the driving force τ3 is smoothed by composing the electromagnet by two coils 13a and 13b and respectively shifting phases of voltages applied to the two coils about 180°, the fluctuation of the driving force characteristic caused by duty control which has been a problem in prior art can be reduced.