There are conventional buckles of this type where a male member in plate form has an elastic piece (engaging piece) of which the end makes contact with the inner surface of a front plate portion of a female member in flat cylindrical form in an elastically deformed state as the male member is inserted into the female member, and the front plate portion of the female member is provided with a hooking portion (engaging portion) for hooking the end portion of the elastic piece in such a manner that an operating piece that is provided in the female member can be pressed inward through operation, and thereby, the elastic piece is elastically deformed in such a direction that the hooked (engaged) state with the hooking portion is released (see for example Patent Document 1).
[Patent Document 1] Japanese Unexamined Patent Publication 2000-106 (page 6, FIG. 19)