PURPOSE: To ensure the prevention of abrasion powder dispersion and simplify the maintenance of the inside of a cover mounted for preventing the abrasion powder dispersion by providing an abrasion powder adsorbing agent in the surrounding atmosphere of a position where the arrival of the powder generated at a slipping section is desirably avoided.

CONSTITUTION: A signal is transferred from a detector or the like, due to the contact of a ring 4 fitted to a stationary section with a brush 5 fitted to a rotary section in a low pressure slipping section. Abrasion powder generated at the time of the contact is adsorbed by an abrasion powder adsorbing material 7 fitted to the inside of an abrasion powder dispersion preventive cover 6. This cover 6 is mounted on the rotary section, together with the brush 5, and rotates around the ring 4. As the adsorbing material 7, cloth, a foamed material, an adhesive tape, a raising material or the like is used, and screwed to the cover 6 with a retainer 8.