A female coupling member is provided which includes locking members (32) for securing the female coupling member to a male coupling member (12) inserted into a receiving portion (22) thereof. The receiving portion has an inner surface (35-2) that slidingly engages a forward end outer surface (12-2) of the male member (12) when the male member is inserted into the receiving portion (22) and before it reaches a position where the male and female members are secured to one another by the locking members (32). The receiving portion further has a forward end inner surface (20-1(2)) that slidingly engages an outer surface (12-3) of the male member that is more rearward of the forward end outer surface (12-2) than the engaging portion (12-1) of the male member when the inward inner surface slidingly engages the forward end outer surface (12-2) of the male coupling member.