A relay device includes a first rotor having an inner cylinder, a second rotor having an outer cylinder and a cover attached to the inner cylinder. A flexible flat cable is accommodated in an annular space defined between the inner cylinder and the outer cylinder. The inner cylinder is provided with a shroud part for retaining the end portion of the flexible flat cable therein while the cover is provided with a press part. The press part is arranged so that, when the cover is attached to the inner cylinder, the press part is brought into contact with the shroud part from the outside. Therefore, the press part urges the inner end portion of the cable against the inner cylinder, whereby the inner end portion of the cable can be fixed on the inner cylinder securely.