An upper portion of a footwear is detachably attached, the attached upper portion is sufficiently prevented from being removed, and the footwear can be thinner. To attach an upper portion (5) on an outsole portion (3), a plurality of insertion pieces (15) made of a material having elasticity is formed on a periphery of the upper portion (5). A locking hole (19) is formed on each of the insertion pieces (15). Insertion holes (21) are formed on the outsole portion (3) at a position of each of the insertion pieces (15) in a state that the upper portion (5) is attached so that the insertion pieces (15) is inserted into and penetrated through the insertion holes (21). Locking protrusions (31) are formed on the outsole portion (3) to lock the locking hole (19) in this state.