Abstract: A sealing device includes a seal lip slidably contacting an outer surface of an inside member and seals liquid in an internal space of an outside member. The seal lip has a liquid-side inclined surface, an atmosphere-side inclined surface, and a lip edge between the liquid-side and atmosphere-side inclined surfaces and extending circumferentially. Helical ribs contacting the outer surface of the inside member are on the atmosphere-side inclined surface, and incline relative to the lip edge. Each rib has a linear portion having parallel side walls and a ship-bottom-shaped portion curving to expand further than the side walls, the linear portion extends from the lip edge, and the ship-bottom-shaped portion is farther from the lip edge than the linear portion. A height of each linear portion relative to the atmosphere-side inclined surface is 5 ?m to 37 ?m.