Abstract: A small-size piping coupling joint, comprising a retainer member with a piping insertion hole perforated in a shaft center portion of a bottom wall and a plurality of locking claw walls projecting uniformly as tapered toward a rear side provided on a peripheral side wall portion, and a socket member provided with a flow hole in the shaft center portion ranging to a stepped expanded portion inside of an end portion on a coupling side, and having an engaging groove on an outer circumferential wall portion. With an outward swelling wall having a seal ring on the back positioned within the stepped expanded portion, the retainer member and the socket member are locked overlapping each other to connection, thus the locking claw walls are locked resiliently in the engaging groove on the socket member side to coupling of the piping.