A method for assembling a roller bearing having rollers and spacers interposed between the adjacent rollers includes alternately disposing, along the inner circumference of an outer ring, the rollers and the spacers. Two spacers are then placed along inner portions of rolling contact surfaces of the rollers having been disposed. The last roller is then inserted toward the outer ring so that the spacers placed on both sides are allowed to slide, whereby the last roller is mounted on the inner circumference of the outer ring.