PURPOSE: To make the contact resistance small to transmit a low voltage large electric current by interposing an electric conductive liquid between a rotation center axis of a rotary portion and a cylindrical portion of a stationary portion.

CONSTITUTION: A cylindrical rotary-portion electrode 3 is mounted on a rotation- center axis 2 of a rotary portion 1 via an insulator 4 interposed between the electrode 3 and the rotary portion 1. With respect to a stationary portion 5, a cylindrical stationary electrode 6 is mounted on the center axis 2 via the insulator 4. Between the electrodes 3 and 6 mercury 7 is filled while lead wires 8 are connected thereto for take-out of electricity. The rotary portion 1 is rotatably supported by a holding mechanism and the rotary-portion 1 side lead wire 8 is connected to a device which rotates jointly with the rotary portion 1. Then, an electric current forwardly flows in the order of the electrode 3, mercury 7 and electrode 6, or reversely flows in the reverse order and the contact resistance between the rotary portion 1 and the stationary portion 5 becomes small. With this, electrification of a low voltage large electric current becomes possible and resistance variation due to the rotation is eliminated. Thus, it becomes easy to make control of a very small angle of rotation.