Each separator is interposed between two cylindrical rollers next to each other in the circumferential direction of a cylindrical roller bearing. A first concave surface on which the cylindrical roller slides and a first groove are formed in a first end surface that is one end surface of the separator in the circumferential direction. The first groove opens at one end of the separator in the axial direction of the roller bearing, and opens at one end of the separator in the radial direction of the roller bearing. When the separator is fitted to the roller bearing, the first groove opens toward a first rib of the inner ring in the axial direction, and opens toward the outer peripheral cylindrical raceway surface in the radial direction.