A protecting cap is used for protecting a plurality of terminals disposed in a cylindrical portion of an electrical connector to be inserted in a mounting hole formed in a panel so that an open end of the cylindrical portion faces the mounting hole. The protecting cap is attached to the open end of the cylindrical portion. The protecting cap includes a lid portion covering the open end of the cylindrical portion of the connector and a pair of engagement members attaching the lid portion to the cylindrical portion of the connector. The lid portion has inclined faces so that the lid portion tapers in a direction away from the open end of the cylindrical portion. Since the protecting cap is tapered, it can be readily inserted into the mounting hole. Upon insertion of the distal end of the cap into the mounting hole, the connector can be guided to a normal position even when it is positionally offset relative to the mounting hole.