Safety device for sealed battery and sealed battery using it

A safety device for a closed battery capable positively preventing a rupture due to a rapid internal pressure rise at over-packing and short-circuiting and being produced inexpensively, a positive electrode lid (16 ) attached to one end of an outer covering can (11 ) comprises a pressure receiving plate (18 ) forming the innermost lid and connected to positive electrode (13 ) of an electrode unit (12 ) via positive electrode lead (17 ), a shielding plate (20 ) forming a middle lid and electrically connected to the pressure receiving plate (18 ) via a center contact (19 ), and a sealing plate (21 ) forming the outermost lid and electrically connected to the shielding plate (20 ). The center contact (19 ) is formed of a projection (28 ) having a first flat contact surface (27 ) of the pressure receiving plate (18 ) and a second flat contact surface (29 ) of the shielding plate (20 ), and a plurality of annular grooves (31, 33 ) are alternately provided around the second flat contact surface (29 ) so as to face each other at 180° intervals, the annular grooves (31, 33 ) being covered with a metal foil (34 ) to form valve membranes (35, 36 ).