A valve device includes a float constituting a lower valve body and a case accommodating the float, and constitutes a part of an airflow passage of a fuel tank. The valve device includes a top portion of the case formed with a first penetration hole, a cylindrical seal body with a part that is fit in the first penetration hole and is sandwiched between the top portion and a sandwich member having a second penetration hole and combined with the top portion from above the top portion, an inside of the seal body communicating with the second penetration hole of the sandwich member, and an upper valve body above the sandwich member and configured to open and close the second penetration hole.