An outsole includes a substantially flat reference surface formed on a lower side of the outsole, and studs projecting downward from the reference surface and each having a projection surface positioned below the reference surface. Midsole hollows are provided in a lower portion of a midsole. The midsole hollows are each defined between an upper portion of the outsole and an associated one of midsole recesses formed in a lower surface of a lower midsole at positions facing upper sides of the studs.