A connector housing has an opening for pressure contacting an insulated wire to an insulation displacing terminal in a terminal accommodating chamber. A housing body has an upper wall and a lower wall one of which defines the opening. A cover is for closing the opening and is connected integrally to the housing body through a hinge. An engagement projection is fixed to an outer surface of the cover at a position opposite to the hinge. When a set of insulation-displacement connectors is joined, the engagement projection is fitted in an engagement recessed part formed on an opposing surface of a mating connector, so that the connector housing and the mating connector are joined with each other. Insulation-displacement connectors are stacked in a vertical direction and each has the engagement projection formed to the cover.