A sealing structure of a multicore cable comprising: the multicore cable including a plurality of electric wires (13A, 13B, 13C, 13D), characterized by: a sheath configured to cover the plurality of electric wires (13A, 13B, 13C, 13D); a rubber stopper fitted on an end of the sheath and including a plurality of through holes (22A, 22B, 22C, 22D) through which the plurality of electric wires (13A, 13B, 13C, 13D) are passed, respectively; a cap fitted on the rubber stopper and pressing the rubber stopper inward; and a holder including a sheath holding portion for holding the sheath and a cap holding portion for holding the cap, wherein the holder includes a first holder and a second holder fitted together, the sheath holding portion includes a first sheath holding portion included in the first holder and a second sheath holding portion included in the second holder, and at an end of the sheath holding portion closer to the cap holding portion or a portions of the sheath holding portion adjacent to the end closer to the cap holding portion, position guide ribs (61C, 61D) are formed at portions of the first sheath holding portion and the second sheath holding portion that are opposed to each other so as to protrude inward and extend along a circumferential direction of the sheath when the sheath is placed in the sheath holding portion. the multicore cable including a plurality of electric wires (13A, 13B, 13C, 13D), characterized by: a sheath configured to cover the plurality of electric wires (13A, 13B, 13C, 13D); a rubber stopper fitted on an end of the sheath and including a plurality of through holes (22A, 22B, 22C, 22D) through which the plurality of electric wires (13A, 13B, 13C, 13D) are passed, respectively; a cap fitted on the rubber stopper and pressing the rubber stopper inward; and a holder including a sheath holding portion for holding the sheath and a cap holding portion for holding the cap, wherein the holder includes a first holder and a second holder fitted together, the sheath holding portion includes a first sheath holding portion included in the first holder and a second sheath holding portion included in the second holder, and at an end of the sheath holding portion closer to the cap holding portion or a portions of the sheath holding portion adjacent to the end closer to the cap holding portion, position guide ribs (61C, 61D) are formed at portions of the first sheath holding portion and the second sheath holding portion that are opposed to each other so as to protrude inward and extend along a circumferential direction of the sheath when the sheath is placed in the sheath holding portion. a sheath configured to cover the plurality of electric wires (13A, 13B, 13C, 13D); a rubber stopper fitted on an end of the sheath and including a plurality of through holes (22A, 22B, 22C, 22D) through which the plurality of electric wires (13A, 13B, 13C, 13D) are passed, respectively; a cap fitted on the rubber stopper and pressing the rubber stopper inward; and a holder including a sheath holding portion for holding the sheath and a cap holding portion for holding the cap, wherein the holder includes a first holder and a second holder fitted together, the sheath holding portion includes a first sheath holding portion included in the first holder and a second sheath holding portion included in the second holder, and at an end of the sheath holding portion closer to the cap holding portion or a portions of the sheath holding portion adjacent to the end closer to the cap holding portion, position guide ribs (61C, 61D) are formed at portions of the first sheath holding portion and the second sheath holding portion that are opposed to each other so as to protrude inward and extend along a circumferential direction of the sheath when the sheath is placed in the sheath holding portion.