A connector, which is attached into an attaching hole formed on a panel body and has an engagement waiting state and a complete engagement state, comprises a first connector housing, a cover member for accommodating the first connector housing so as to be slidable in an engagement direction, a holder for accommodating the cover so as to be engaged therewith provisionally under the engagement waiting state and so as to be slidable in the engagement direction under the complete engagement state, the holder includes at least one pair of stoppers stacking on rear face of the panel body in a peripheral portion of the attaching hole, at least one pair of flexible engagement members elastically abutting against a front face of the panel body in the peripheral portion of the attaching hole and at least one pair of alignment members elastically fitted into the attaching hole; and a second connector housing to be engaged with the first connector housing.