In a self-aligning roller bearing, in a longitudinal section including a center line of a spherical roller and an axis of the self-aligning roller bearing, a clearance X between an outer end surface of a spherical roller on an axially outer side of the self-aligning roller bearing and a rib portion, and a clearance Y between an inner end surface of the spherical roller on an axially inner side of the self-aligning roller bearing and a guide ring have a relation of X