A gas-leak-detection device for detecting a gas leakage from an evaporative emission system includes an electric-wire-connection portion and a passage connection portion that are disposed to overlap with at least one of appearance components in a vehicle when the vehicle is seen in a viewing direction, and are disposed closer to the at least one appearance component than a center plane perpendicular to the viewing direction when the vehicle is in an upright state, the center plane being one of an imaginary-lateral-center plane that is an imaginary vertical plane perpendicular to the left-right direction, an imaginary-longitudinal-center plane that is an imaginary vertical plane including a center in the front-rear direction and being perpendicular to the front-rear direction, or an imaginary-vertical-center plane that is an imaginary horizontal plane including a center in the top-bottom direction and being perpendicular to the top-bottom direction.