Disclosed is a coin battery including: a cylindrical battery can having a bottom portion, and a first side wall rising from the periphery of the bottom portion; a sealing plate having a top portion, and a second side wall extending from the periphery of the top portion along the inner side of the first side wall; a gasket interposed and compressed between the first side wall and the second side wall; and a power generation element sealed with the battery can and the sealing plate. In order to improve the battery capacity while ensuring leakage resistance, the second side wall is provided with a bulging portion bulging outward, and a part of the power generation element is disposed inside the bulging portion. The negative electrode is preferably in contact with the inner side of the bulging portion.