Grooves (39) are formed in locking projections (38) provided on side surfaces of an auxiliary connector (30), and disengaging projections (27) which can enter the grooves (39) project from locking surfaces (26A) of locking pieces (26) provided on inner side walls of an accommodating portion (12). The locking piece (26) can be disengaged form the corresponding locking projection (38) by pressing an introducing surface (27A) of the disengaging projection (27) in the groove (39) by means of a jig (J) to resiliently deform the locking piece (26). Since the locking pieces (26) can be made smaller than prior art ones, deformation spaces therefor can also be made smaller, which enables the miniaturization of a housing main body (11) or the miniaturization of male and female connectors (50, 10).