When a control retainer and a rotary retainer rotate relative to each other, a plurality of pairs of rollers received in respective pockets are pushed by pillars so as to move to their disengaged position. An anti-rotation arrangement is provided between an outer ring and the control retainer. The anti-rotation arrangement prevents the control retainer from rotating relative to the outer ring when the rollers are engaged, so that that the rollers does not move to their neutral position. This increases reliability. The anti-rotation arrangement includes a plurality of first protrusions formed on the surface of the outer ring, and a plurality of second protrusions formed on the surface of the control retainer axially opposed to the surface of the outer ring. Heat treatment is performed to the first and second protrusions so as to increase the hardness thereof.