Abstract: Provided is a buckle including a plug and a socket. The plug includes a pair of leg portions, each of which is provided with an engaging portion, and outer and inner leg pieces extending while opposing each other. In the vicinity of a distal end portion of the leg portion, the outer and inner leg pieces are connected to each other by a distal end connection portion. On a base end portion of the leg portion, the outer and inner leg pieces are connected to each other by an arm portion. Opposing arm distal end portions of the arm portions are formed to define a slit having a predetermined space between the leg portions. The opposing arm distal end portions are connected to guide portions extending in a protruding direction of the leg portions. The pair of leg portions is provided to be swingable across the slit.