The present invention aims to provide a method for manufacturing a prismatic sealed cell having a good reliability of sealing. This object is realized with the following configuration.The method of manufacturing a sealed cell comprises the following steps: fitting a substantially planar rectangular sealing plate to the opening of a prismatic outer casing; and irradiating a high energy beam so that the spot center of the beam is shifted (offset) from the fitted portion to the sealing plate side in order to seal the sealing plate and the outer casing.In this method, the maximum distance from the outer periphery the sealing plate to the spot center at the four corners of the sealing plate is longer than the distance from the outer periphery of the sealing plate to the spot center at a linear portion of the sealing plate.