a breather valve connected to a breather passage for opening and closing a valve element to adjust the internal pressure of a sealed container corresponding to the pressure change inside the sealed container includes a valve bore , the valve element slidably fitted in the valve bore , a spring for pushing the valve element toward the sealed container , an elastic portion tapering toward the sealed container , a slit formed at the free end of the elastic portion , and a needle member extending from the side opposite to the sealed container toward the slit . plastic deformation caused by pressure reduction inside the sealed container opens the slit while the needle member projects through and opens the slit when increase of the internal pressure of the sealed container pushes the valve element against the pressure of the spring .