A sealing structure 12 of a multicore cable 11 includes the multicore cable 11, a rubber stopper 15, a cap 17, and a holder 52. The multicore cable 11 includes first to fourth electric wires 13A, 13B, 13C and 13D covered with a sheath 14. The rubber stopper 15 is fitted on an end 14A of the sheath 14 and first to fourth through holes 22A, 22B, 22C and 22D through which the first to the fourth electric wires 13A, 13B, 13C and 13D are passed, respectively. The cap 17 is fitted on the rubber stopper 15 and presses the rubber stopper 15 inward. The holder 52 includes a sheath holding portion 60 for holding the sheath 14 and a cap holding portion 62 for holding the cap 17.