A tapered roller bearing including: an inner ring; an outer ring provided on an outer peripheral surface of the inner ring via an annular space so as to be disposed on the same center line as the inner ring; a plurality of tapered rollers rollably disposed in the annular space; and a cage retaining the plurality of tapered rollers, the tapered roller bearing being configured such that liquid lubricant flows through the annular space; among the inner ring, the outer ring, the tapered rollers, and the cage, at least one rotating component configured to rotate at the time of bearing rotation is provided with a vaporization promotion mechanism configured to decrease a pressure of the lubricant at the time of bearing rotation so that the pressure of the lubricant reaches a saturation vapor pressure at which the lubricant changes from a liquid phase to a vapor phase, characterized in that the vaporization promotion mechanism is constituted by roller vaporization promotion portions formed in the tapered rollers, the roller vaporization promotion portions are each formed from a plurality of grooves extending axially and formed in a noncontact region (54, 55) of an outer peripheral surface of each of the tapered rollers, the noncontact region being a region outside an effective rolling region of the outer peripheral surface of the each of the tapered rollers, the vaporization promotion mechanism is configured such that when the liquid lubricant flows through the annular space between the inner ring and the outer ring at the time of bearing rotation; at this time, the pressure of the lubricant is decreased by the roller vaporization promotion portions, so that the pressure of the lubricant reaches the saturation vapor pressure at which the lubricant changes from the liquid phase to the vapor phase, thereby causing vapor cavitation, at the time of bearing rotation, a low-pressure part occurs behind a groove wall surface out of both groove wall surfaces of the groove; and/ or the vaporization promotion mechanism is provided in the cage, the cage includes an annular portion (61, 62), bar portions extending axially from the annular portion (61, 62), and pockets constituted by the annular portion (61, 62) and the bar portions, each of the bar portions includes a bore-side extending portion extending inwardly in a radial direction, and an outside extending portion extending outwardly in the radial direction, a rear wall surface of the bar portion including the bore-side extending portion and the outside extending portion, in terms of a rotation direction of the cage, is formed generally perpendicularly to the rotation direction, a bore surface of the bore-side extending portion is provided close to an inner-ring raceway surface of the inner ring with a bore-side gap portion which is a minute gap, and an outside surface of the outside extending portion is provided close to an outer-ring raceway surface of the outer ring with an outside gap portion which is a minute gap, the vaporization promotion mechanism is constituted by a combination of the rear wall surface, the bore-side gap portion, and the outside gap portion, the vaporization promotion mechanism is configured such that when the liquid lubricant flows through the annular space between the inner ring and the outer ring at the time of bearing rotation; at this time, the pressure of part of the lubricant reaches the saturation vapor pressure at which the lubricant changes from the liquid phase to the vapor phase, due to the vaporization promotion mechanism provided in the cage, thereby causing cavitation in the lubricant, at the time of bearing rotation, a region where low-pressure parts (90, 91) occur is increased behind the rear wall surface of the bar portion; and/ or the vaporization promotion mechanism is provided in a rotation-side bearing ring configured to rotate at the time of bearing rotation, the rotation-side bearing ring being either one bearing ring out of the inner ring and the outer ring, the vaporization promotion mechanism is configured such that when the liquid lubricant flows through the annular space between the inner ring and the outer ring at the time of bearing rotation, at this time, due to the vaporization promotion mechanism provided in that rotation-side bearing ring configured to rotate at the time of bearing rotation which is either one bearing ring out of the inner ring and the outer ring, the pressure of part of the lubricant reaches the saturation vapor pressure at which the lubricant changes from the liquid phase to the vapor phase, thereby causing cavitation in the lubricant, the vaporization promotion mechanism is constituted by axial recessed portions or projection portions formed in rib portions (33, 35) of the rotation-side bearing ring, and at the time of bearing rotation, a low-pressure part occurs behind a groove wall surface out of both groove wall surfaces of each of axial recessed portions or projection portion formed in rib portions (33, 35) of the rotation-side bearing ring placed at a front side in a rotation direction.