The invention provides a square secondary battery with high reliability. The square secondary battery is equipped with an electrode body (3) including a positive electrode plate and a negative electrode plate, a square outer package (3) housing the electrode body (3), a metal sealing plate (2) sealing an opening of the square outer package, and a positive electrode collector (6) electrically connected to the positive electrode plate (6) and the sealing plate (2). The positive electrode collector (6) includes a base portion (6a) disposed to oppose the sealing plate (2), and a lead portion (6b)extending from an edge portion of the base portion (6a) towards the electrode body (3). In a short direction of the sealing plate (2), a boundary (40) between the base portion (6a) and the lead portion (6b) is positioned on a first side with respect to a center of the sealing plate (2), and a connection between the sealing plate (2) and the base portion (6a) of the positive electrode collector (6)is offset to a second side with respect to the center of the sealing plate (2).