A shoe sole comprising: a plate forming a part of a shoe, the plate comprising a curved portion located in a forefoot region of the shoe sole, the forefoot region overlapping, in a thickness direction of the shoe sole, a forefoot portion of a wearer of the shoe, the curved portion being shaped to curve toward a flat plane, in the shoe sole placed on the flat plane; a midfoot supporting portion located in a midfoot region of the shoe sole, the midfoot region overlapping, in the thickness direction, a midfoot portion of the wearer, the midfoot supporting portion supporting the midfoot portion; and a rear-foot supporting portion located in a rear foot region of the shoe sole, the rear foot region overlapping, in the thickness direction, a rear foot portion of the wearer, the rear-foot supporting portion supporting at least a part of the rear foot portion, wherein the curved portion has a wide region including a wide portion of which dimension in a width direction is largest in the curved portion, the midfoot supporting portion has a narrow region including a narrow portion of which dimension in the width direction is smallest in the midfoot supporting portion, and a ratio of a bending rigidity of the narrow region to a bending rigidity of the wide region is 0.4 or more and 0.85 or less, wherein the bending rigidity is rigidity against bending on a straight line that is parallel to the longitudinal direction of the shoe, wherein the shoe sole further comprises a midsole including the forefoot region, the midfoot region, and the rear foot region, wherein the plate is placed within the midsole in such a manner that the curved portion is located in the forefoot region and the midfoot supporting portion is located in the midfoot region, the midsole includes: a lower midsole placed under the plate; and an upper midsole placed over the plate, the lower midsole includes a supporting portion that supports an entire area of the curved portion, the supporting portion is elastically deformable to allow the curved portion to deform in such a manner that reduces a curvature of the wide region, a thickness of a part of the supporting portion that overlaps the plate in the thickness direction and overlaps, in the thickness direction, at least a part extending frontward from the wide portion is constant, and the lower midsole supports the plate in such a manner that the part of the plate that extends rearward from the curved portion has a posture separated gradually further away from the flat plane, toward a rear in the longitudinal direction of the shoe. a plate forming a part of a shoe, the plate comprising a curved portion located in a forefoot region of the shoe sole, the forefoot region overlapping, in a thickness direction of the shoe sole, a forefoot portion of a wearer of the shoe, the curved portion being shaped to curve toward a flat plane, in the shoe sole placed on the flat plane; a midfoot supporting portion located in a midfoot region of the shoe sole, the midfoot region overlapping, in the thickness direction, a midfoot portion of the wearer, the midfoot supporting portion supporting the midfoot portion; and a rear-foot supporting portion located in a rear foot region of the shoe sole, the rear foot region overlapping, in the thickness direction, a rear foot portion of the wearer, the rear-foot supporting portion supporting at least a part of the rear foot portion, wherein the curved portion has a wide region including a wide portion of which dimension in a width direction is largest in the curved portion, the midfoot supporting portion has a narrow region including a narrow portion of which dimension in the width direction is smallest in the midfoot supporting portion, and a ratio of a bending rigidity of the narrow region to a bending rigidity of the wide region is 0.4 or more and 0.85 or less, wherein the bending rigidity is rigidity against bending on a straight line that is parallel to the longitudinal direction of the shoe, wherein the shoe sole further comprises a midsole including the forefoot region, the midfoot region, and the rear foot region, wherein the plate is placed within the midsole in such a manner that the curved portion is located in the forefoot region and the midfoot supporting portion is located in the midfoot region, the midsole includes: a lower midsole placed under the plate; and an upper midsole placed over the plate, a lower midsole placed under the plate; and an upper midsole placed over the plate, the lower midsole includes a supporting portion that supports an entire area of the curved portion, the supporting portion is elastically deformable to allow the curved portion to deform in such a manner that reduces a curvature of the wide region, a thickness of a part of the supporting portion that overlaps the plate in the thickness direction and overlaps, in the thickness direction, at least a part extending frontward from the wide portion is constant, and the lower midsole supports the plate in such a manner that the part of the plate that extends rearward from the curved portion has a posture separated gradually further away from the flat plane, toward a rear in the longitudinal direction of the shoe.