According to the present invention, in a battery can forming a container or cover of a sealed type battery, a cruciform incision is made on a metal plate forming the battery can. Said incision being V-shaped in cross-section and the cruciform intersection point being constructed to present an X-shaped, wedge-shaped tip as seen in the view plan forming a thin part in the metal plate so that, when the internal pressure of the battery becomes abnormally high, before the sealed part is opened, by the pressure the thin part may tear and open to let the abnormal pressure escape and prevent the explosion and bursting of the battery.By such construction, the fluctuation of the pressure resisting the tearing and opening of the above mentioned thin part can be reduced and a safe and positive operation can be made.