A ball transfer unit comprising a body in a seat face recessed in a semispherical shape is formed, a plurality of small balls rollingly in contact with the seat face of the body, a large ball rollingly in contact with the plurality of small balls, and a cover fitted to the body to hold the large ball and hold the small balls between the large ball and the seat face of the body. At least the body and the large ball are formed of either of PAI, PBI, PCTFE, PEEK, PEI, PI, PPs, melamine resin, aromatic polyamide resin, aluminum oxide, zirconium oxide, and silicon nitride.