To provide seal structure of a connector for restraining satisfactorily a sealing portion from being corroded caused by deposit of a liquid droplet of a saline solution.

This waterproof structure of the connector 13 engaged, from an upper side, with an engagement port 11 formed in a case 10, includes a sealing member 12 interposed in an engagement portion of the case 10 with a connector 13, and an outer edge part 14 and a dropping-down part 15 provided in the connector 13, and for guiding the liquid droplet deposited on an outer circumference of the connector 13, toward a portion other than the engagement portion.