Side release buckle and lock member for same

A side release buckle comprising:

• a plug;
• a socket into which the plug is inserted for engagement;
• and
• a lock member being attachable to the socket to double-lock the plug, wherein the plug comprises:
• a plug base comprising a belt attachment;
• a pair of legs projecting from the plug base;
• and
• engaging portions being formed on the legs, respectively, the socket comprises:
• a socket body comprising a belt attachment and an insertion opening;
• a housing space being defined in the socket body and in which the legs inserted through the insertion opening are housed;
• engaged portions being formed on the socket body and being engageable with the engaging portions, respectively;
• and
• a cutout being formed from an edge of the belt attachment toward the insertion opening,
• the lock member comprises:
• a plate-shaped base portion being positioned on a top side of the socket;
• a holder being configured to retain the base portion relative to the socket;
• an operating portion being connected to the base portion and being movable in a direction intersecting the base portion by an external operation;
• and
• a lock portion being configured to restrict disengagement between the engaged portions and the engaging portions,
• the operating portion comprises a cantilever being continuous with the base portion and being swingable relative to the base portion, and
• the lock portion is positioned in the socket and is connected to the operating portion via a joint that is to be inserted in the cutout of the socket, the lock portion being present in movement paths along which the engaging portions move to be disengaged from the engaged portions without the external operation on the operating portion, the lock portion being moved away from the movement paths when the operating portion is moved by the external operation.