To provide a roller bearing and its installation structure, easy in assembling, and capable of using an outer ring of a shape distorted from a normally unusable cylindrical shape as it is.

This roller bearing 1 has a raceway surface for receiving a roller 4 on an inner peripheral surface, and is divided into two parts in the peripheral direction, and includes the outer ring 20 formed in a cylindrical shape by combining these divided pieces, and is characterized in that the divided pieces 2 and 3 are dividedly formed by cutting a cylindrical raw material for constituting the outer ring 20 in the axial direction, and cutout recessed parts 2H and 3H cut out in the peripheral direction from dividing surfaces, are arranged on the respective opposed dividing surfaces of its pair of divided pieces 2 and 3, and the cutout recessed parts 2H and 3H are constituted as an insertion hole forming part for forming an insertion hole for inserting a positioning pin when forming the outer ring 20 by combining the divided pieces 2 and 3.