In a shielded structure of a flat shielding electric wire, the flat shielding electric wire includes a plurality of shielding cores, an inner insulating sheathe covering each of the plurality of shielding cores, a conductive covering member covering the inner insulating sheathes, and a first outer insulating sheathe covering the conductive covering member. A pair of resin members sandwiches the flat shielding electric wire therebetween. A coating electric wire is provided between the flat shielding electric wire and one of the pair of resin members. The coating electric wire includes a conductive wire and a second outer insulating sheathe covering the conductive wire. The first outer insulating sheathe and the second outer insulating sheathe are fused by ultrasonic excitation so that the conductive wire is electrically connected to a part of the conductive covering member. At least one of the pair of resin members is formed with an ultrasonic attenuation groove so as to face at least a part of the second outer insulating sheathe.