In a wafer polishing apparatus which polishes a wafer surface or in a wafer cleaner, there are provided a transfer and cleaning chamber which shuts off a wafer from the outside air and an inert gas supply device which fills an inert gas into the transfer and cleaning chamber. The rotation mechanism includes a rotary shaft, and a support unit that supports the rotary shaft rotatably through a bearing and sealing member. A carrier plate is mounted within the cover, at a distance therefrom, on which are provided an active guard electrode in respect of the sense electrode and a grounded shield member in respect of the emitter electrode. The distributor body has an opening at the top for allowing the lubricant in, and has at least two distributor bores disposed on the circumference but offset axially from one another. Other embodiments are described and claimed.