is provided opposite to the inner circumferential surface of the annular protrusion 91 and the free end 91 c of the annular protrusion 91 extends leftward beyond the cover member 71 the outer peripheral edge 73 a of the outer periphery 73 of the cover member 71 is loosely received in an annular groove 92 formed inside the annular protrusion 91 in the guide roller 1 of the third embodiment the fluid mixed with an abrasive intruding into shaft hole 50 from the outer periphery of the housing 4 is guided radially outward or away from the shaft hole 50 as the fluid advances across the annular protrusion 91 provided at the opening end of the shaft hole 50 under the centrifugal force caused by the rotation of the housing 4 in particular the fluid that has reached inside the annular protrusion 91 or the gap between the annular protrusion 91 and the cover member 71 is guided along the tapered inner circumferential surface 91 b to the free end 91 c of the annular protrusion 91 outward from the housing 4 so that the intrusion of the fluid into the shaft hole 50 can be effectively prevented the air pressure supply passage 81 see fig1 was omitted in the guide roller 1 of the third embodiment illustrated in fig6 according to this arrangement the intrusion of cutting fluid mixed with an abrasive can be effectively prevented.