To provide a power transmission system that solves the problem that its gear part for increasing, keeping uniform or reducing the speed has been the cause of vibrations, noises, etc. in the conventional handpiece of a dental micromotor.

The handpiece of a dental micromotor is characterized in that for transmitting rotational power to a dental cutting tool, the handpiece employs a rotational power transmission means that composed of a first rotational member 3 having a magnetic body where the S- and N-poles are continuously and alternately arranged around its external circumferential surface, and a second rotational member 4 having a magnetic body where the S- and N-poles are continuously and alternately arranged in a contact or non-contact state to enable an unlike-pole magnetic force transmission through their respective outer circumferential surfaces.