Electric transmission device in relatively rotating parts

An electric transmission device comprising:

• a pair of first and second magnetic elements relatively rotatable about the same axis, wherein
• the first and second magnetic elements, each comprises a core and a coil having a conductive wire, one of the coils of the first and second magnetic elements being located at an inner side of the other coil in a radial direction with respect to the axis, the coils being configured to be magnetically coupled to each other, the magnetic coupling enabling electric power and/or an electric signal to be transmitted,
• the first and second magnetic elements further comprise respective first and second bobbins, the first and second bobbins being located so as to be concentric with the axis,
• the first and second bobbins each comprises a bobbin cylinder and a disk-shaped bobbin flange, the bobbin cylinder extending in an axial direction that is a direction of the axis and having an outer circumference on which the conductive wire of the corresponding coil is wound, the disk-shaped bobbin flange extending radially outward from at least one end portion of the bobbin cylinder, and
• the bobbin flanges of the first and second bobbins are slidably in contact with each other at contact surfaces in the axial direction of the bobbin flanges, the contact surfaces opposing each other in the axial direction.