A female connector (F) is formed such that a block-shaped terminal accommodating portion (21) accommodating female terminal fittings (24) is surrounded by a substantially rectangular tubular fitting (35). A male connector (M) includes a rectangular tubular receptacle (11) to be fit into a clearance between the terminal accommodating portion (21) and the tubular fitting (35) and tabs (13) at the leading ends of male terminal fittings (12) are surrounded by the receptacle (11). Bulges (51, 52 and 53) are formed on four wall portions (37, 38 and 39) of the tubular fitting 35 and bulge outward of the tubular fitting (35) from an opening edge part at a front side of the tubular fitting (35).