A buckle includes a male member including a base part and a pair of flexible arms extending from the base part, and a female member including an insertion hole formed at one end portion thereof. The pair of flexible arms is inserted in the insertion hole. The base part contacts the one end portion when the male member engages the female member. An outer face portion of each of the pair of flexible arms has a shape curving outwardly at a middle portion thereof relative to an insertion direction of the pair of flexible arms, and the pair of flexible arms is provisionally fastened to the female member when the pair of flexible arm is inserted in the insertion hole.