A sole structure is provided that can improve bendability and cushioning ability of the sole forefoot portion. The sole assembly 1 is formed of an upper plate 2, and a lower plate 3 provided below the upper plate 2 and spaced apart from the upper plate 2 via a void S. The lower plate 3 has a plurality of protrusions 30 that protrude toward the upper plate 2. The longitudinal path length L.sub.1 of the lower plate 3 is longer than the longitudinal path length L.sub.2 of the upper plate 2. More specifically, the path length L.sub.1 of the lower plate 3 is 40-60% longer than the path length L.sub.2 of the upper plate 2.