To extend the upper limit of rotating speed of a rotaing guide of a guide tool so as to be able to reduce the starting torque of the rotating guide.

A bearing unit B is interposed between a shaft body installed out of rotation, and a rotating guide 2. The bearing unit B is so constituted that a first rolling element row 7 with a set of rolling elements 8 arranged around the shaft body 1, and a second rolling element row 11 with a set of rolling elements 12 arranged around the first rolling element row 7 are mounted inside being piled in the radial direction of the shaft body 1. Rotational torque reducing effect obtained by combining the respective rotational torque reducing performance of both rolling element rows 7, 11 is displayed by the bearing unit B.