Abstract: A safety valve having a simple structure and a small operating pressure error and configured to maintain a constant pressure in a battery by effectively discharging gas in the battery is provided. A safety valve according to one aspect of the present invention, which is mounted on a battery and operates to maintain a predetermined internal pressure in the battery when the predetermined pressure or more is applied to the battery, includes a main body, a sub body, a cap membrane, and a cover, and a protrusion is formed on an end portion of the cap membrane to be in line contact with an outer surface of the sub body. The main body has a hollow structure formed so that a top communicates with a bottom and a discharge hole in one side surface of an upper portion. The sub body is formed to protrude from an inner circumferential surface of the main body, and a through hole is formed in one side surface of a lower portion of the sub body.