Abstract: An object of the present invention is to provide a seal structure capable of maintaining necessary sealing performance for a long period of time even in an environment where a corrosive solution such as salt water adheres. A seal portion at which seal materials are formed and a fixing portion that fixes a housing and a cover to each other are formed at a joint portion between the housing and the cover constituting a casing. The seal portion and the fixing portion are arranged from an outer edge portion side of the joint portion toward an inside of the casing in order of the seal portion and the fixing portion.