To improve abrasion resistance by a substantial amount, and contact stability in a connecting region at a low cost.

Lubricating oil is applied to at least either a brush member 1 and a commutator 2, and an oil film is formed at the connecting region between the brush member 1 and the commutator 2. The viscosity of the lubricating oil at the application is determined so as to have a level that allows a monomolecular film to be included in the oil film of the lubricating oil. While lubrication properties and sliding properties provided by the lubricating oil are satisfactorily maintained, the permeability of the monomolecular film of the lubricating oil is secured satisfactorily, thus enabling an arc to be reduced. As a result, the production or the like of powder is suppressed, and a stable contact state can be maintained.