A pneumatic tire used with a specified rotation direction, comprising: a tread; a pair of sidewalls extending continuously from the tread inward in a tire radial direction; a pair of beads continuous with the sidewalls inward in the tire radial direction; and at least one ridge (5, 6) on a buttress surface, the buttress surface being a tire outer surface between a tread edge, which is an outermost position of a tread surface formed on the tread in a tire width direction, and an outermost position of a sidewall in the tire radial direction, and the ridge (5, 6) extending from a sidewall side of the buttress surface towards the tread edge and terminating before reaching the tread edge, wherein the tread surface is the portion of the tire that contacts with a flat plate when the tire is mounted on an applicable rim, with specified pressure applied, and then placed perpendicularly on the flat plate while at rest with a load corresponding to the maximum load capability applied, and the ridge (5, 6) includes a steeply inclined surface (5a, 6a), having a high gradient with respect to the buttress surface, inclined forwards in the rotation direction, and a moderately inclined surface (5b, 6b), having a more moderate gradient than the steeply inclined surface (5a, 6a), inclined backwards in the rotation direction, characterised in that the tire further comprises: at least one concavity (7, 8) on the buttress surface in a region adjacent to the tread edge, the concavity (7, 8) opening to the tread surface, being recessed from the buttress surface, and being independent from the ridge (5, 6), a plurality of lug grooves formed on the tread surface and reaching the tread edge, and a shoulder block defined between the plurality of lug grooves, wherein the buttress surface includes a buttress portion which is an extension of the shoulder block in the tire width direction, and wherein the concavity (7, 8) is provided on the buttress portion and positioned in a region towards the tread edge from the ridge (5, 6) in the tire width direction. a tread; a pair of sidewalls extending continuously from the tread inward in a tire radial direction; a pair of beads continuous with the sidewalls inward in the tire radial direction; and at least one ridge (5, 6) on a buttress surface, the buttress surface being a tire outer surface between a tread edge, which is an outermost position of a tread surface formed on the tread in a tire width direction, and an outermost position of a sidewall in the tire radial direction, and the ridge (5, 6) extending from a sidewall side of the buttress surface towards the tread edge and terminating before reaching the tread edge, wherein the tread surface is the portion of the tire that contacts with a flat plate when the tire is mounted on an applicable rim, with specified pressure applied, and then placed perpendicularly on the flat plate while at rest with a load corresponding to the maximum load capability applied, and the ridge (5, 6) includes a steeply inclined surface (5a, 6a), having a high gradient with respect to the buttress surface, inclined forwards in the rotation direction, and a moderately inclined surface (5b, 6b), having a more moderate gradient than the steeply inclined surface (5a, 6a), inclined backwards in the rotation direction, characterised in that the tire further comprises: at least one concavity (7, 8) on the buttress surface in a region adjacent to the tread edge, the concavity (7, 8) opening to the tread surface, being recessed from the buttress surface, and being independent from the ridge (5, 6), a plurality of lug grooves formed on the tread surface and reaching the tread edge, and a shoulder block defined between the plurality of lug grooves, wherein the buttress surface includes a buttress portion which is an extension of the shoulder block in the tire width direction, and wherein the concavity (7, 8) is provided on the buttress portion and positioned in a region towards the tread edge from the ridge (5, 6) in the tire width direction. at least one concavity (7, 8) on the buttress surface in a region adjacent to the tread edge, the concavity (7, 8) opening to the tread surface, being recessed from the buttress surface, and being independent from the ridge (5, 6), a plurality of lug grooves formed on the tread surface and reaching the tread edge, and a shoulder block defined between the plurality of lug grooves, wherein the buttress surface includes a buttress portion which is an extension of the shoulder block in the tire width direction, and wherein the concavity (7, 8) is provided on the buttress portion and positioned in a region towards the tread edge from the ridge (5, 6) in the tire width direction.