of the housing 11 in a manner that the while contact piece portion 34 is permitted to extend convexly outward it is subjected to a slight inward bias this establishes an initial pressure which causes the turned back piece portion 36 to be positioned between the projection 21 and the circuit protective wall portion 50 while being engaged with the projection 21 accordingly initial pressure is applied at 2 places viz the base holding groove 41 and the projection 21 at this time the initial pressure to the contact 13 is fully established the deflection quantity of the contact 13 when plugging and unplugging the connector plug 10 to the socket 24 is reduced whereby the elasticity lowering is maximally suppressed and therefore the initial pressure can be maintained for a long period of time since the part of the contact piece portion 34 which extends out in the external direction is pegged by the projection 21 the bending portion between the contact piece portion 34 and the turned back piece portion 36 is always positioned in the window 12 thus even it is inserted into the socket 24 of small diameter in particular it is such that the plug 10 can be smoothly inserted into the socket 24 after the printed circuit board 27 is fixed on the lower housing 11b the upper housing 11a is fixed in place by screws after upper and lower housings 11a and 11b are secured together the cap 17 inserting the head terminal 18 is screwed on at the tip.