Abstract: Disclosed is a shoe sole comprising an outer sole 1F, 1B, a midsole 2 and a reinforcement device 4 made of a resin plate. The reinforcement device 4 is firmly secured to the underside of an arch portion 2M of the midsole 2. At a medial side 11 and a lateral side 10 of the foot, the reinforcement device 4 is shaped like an arch between separated outer sole parts 1F and 1B. A medial foot portion 43 of the reinforcement device 4 is formed to have a higher hardness than a lateral foot portion 40 of the reinforcement device 4. This allows the reinforcement device 4 to have a greater flexural rigidity in its medial foot portion 43 than in its lateral foot portion 40.