The present invention has completely broken from the unreasonable construction of conventional type of relief valve which places weight and lifting disc inside of upper body or lower body. In other words, lifting disc and weight are placed outside of upper body. It is brand-new construction that adopts casket-shaped housing forming flow slot which guides releasing gas to move upwards vertically when the above-mentioned lifting disc ascends by the releasing gas from tank. And also the present invention features that drain part is formed to drain all the time sea water or rain gathering inside of casket-shaped housing to outside of casket-shaped housing and brand-new construction of vacuum relief valve is equipped.