The spiral electrode rectangular battery has a first electrode plate and second electrode plate, which are the positive and negative electrodes, laminated together with a separator sandwiched in between, rolled into an electrode unit, and housed in an exterior casing. The electrode unit has flat surfaces on opposite sides, and edges on both sides of those flat surfaces are curved with a prescribed radius of curvature to form rounded edge regions. The first and second electrode plates are wound around flat surfaces and rounded edge regions in a continuous fashion, and the end of the outer-most electrode plate is disposed at a rounded edge region. In addition, corner cuts are provided to truncate corner regions formed between the edges at both sides and the end of the outer-most electrode plate.