A roller bearing and a bearing structure, wherein the flange part of an inner ring member (11) used in the roller bearing comprises a thin-wall part (13) with a relatively small radial thickness on its end face side and a thick-wall part (14) with a relatively large radial thickness at the flange part center of the thin-wall part. The inner diameter surface of the flange part comprises a contact part (15) fitted to an axle at its center part, a non-contact part (16) radially apart from the axle formed at its outer edge part, and a ridge line part (17) positioned on a boundary between the contact part (15) and the non-contact part (16). The axial width L1 of the thin-wall part (13) from the end face (12) of the inner ring member (11) and the axial distance L2 of the thin-wall part from the end face (12) of the inner ring member (11) to the ridge line part (17) meet the requirement of L1 L2.