A buckle includes a pair of legs on a male member, and an engagement portion provided on an end of the legs that is to be engaged with an engaged portion of a female member in a form of a recessed groove, the engagement portion being detachably engaged with the engaged portion when the male member is inserted into the female member to a predetermined position. A guide for guiding the insertion of the male member provided between the legs of the male member. A hook-shaped movement restricting portion projecting in the direction for the pair of legs to face with each other is provided on an inner side of the legs. A deformation restricting portion projecting in a form of a flange toward the leg is provided to the guide. The movement restricting portion is in contact with the deformation restricting portion when the leg is outwardly deformed.