An electrical connector casing enclosing an electrical connector comprises a case part having a connector inlet, and a lid part having a lid opening, where the openings of the connector inlet and the lid opening have a substantially the same shape and are angled differently from each other as viewed from a front-back direction. An electric connector is inserted from the back of the lid part through the lid opening, and is rotated to be inserted into the connector inlet from the back of the case part. When the lid part attaches to the case part, due to the rotationally different angles between the lid opening and the connector inlet, the electric connector is securely held inside the casing.