An electrical connector assembly has a fixed connector, a middle connector, and a plug connector. The fixed connector is attached to a circuit member of an electrical device. The middle connector is connected and pulled out to and from the fixed connector in a direction same as that of the plug connector being connected and pulled out to and from the middle connector. Each of the fixed connector, the middle connector, and the plug connector is provided with engagement portions at both end portions thereof in a direction parallel to a straight line extending in a different direction from an insertion and pull-out direction. With the engagement portions, it is possible to prevent the fixed connector from coming off from the middle connector when the plug connector is pulled out.