Provided is a buckle including a plug member and a socket member, wherein the plug member includes lock arms and a guide rod located at a middle position between the lock arms, and the socket member includes a holder formed in a chamber so as to catch the lock arm. The guide rod is provided on the front end thereof with a holding member, and the socket member is centrally provided with a guide groove for the coupling of the guide rod and is also provided with a holding protrusion for the coupling of the holding member. As such, in addition to the coupling between the lock arm and the holder, another coupling structure is provided so as to prevent the buckle from being easily unfastened by unintentional external contact or pressure while ensuring convenient separation of the buckle with one hand as needed.