An explosion-proof valve installed to a hole portion of a pressure vessel and valve opening when the pressure within the pressure vessel goes beyond a predetermined value so as to release the pressure integrally has a tubular portion inserted to the hole portion, an outside flange portion provided in one end portion of the tubular portion and engaging with an opening peripheral edge portion outside the vessel in the hole portion, a locking projection provided in the other end portion of the tubular portion and engaging with an opening peripheral edge portion in side the vessel in the hole portion, and a membrane portion provided in an inner peripheral side of the tubular portion and rupturing due to the pressure at the valve opening time, and has such a shape that an outer diameter of the outside flange portion is made smaller than an outer diameter of the locking projection.