A rotary disk rotatable around a vertical rotation axis; a bearing supporting the rotary disk so as to be freely rotatable; a slide disk slidable on a top surface of the rotary disk; a position adjustment bracket that displaces the slide disk along the top surface of the rotary disk; a placement disk that is supported by the slide disk; a plurality of air nozzles that are arranged on a top surface of the stator in an annular shape centered on the rotation axis, and form a static pressure air film between the top surface of the stator and a bottom surface of the rotary disk; an aerostatic pocket formed between the top surface of the rotary disk and a bottom surface of the slide disk; and a communication aperture is formed on the rotary disk and introduces pressure of the static pressure air film into the aerostatic pocket.