A secondary battery in accordance with the present invention includes a square battery can 1 having a positive electrode terminal and a negative electrode terminal, an electrode assembly 9 arranged in the square battery can having a sheet-shaped positive electrode 2 electrically connected to the positive electrode terminal and a sheet-shaped negative electrode 3 electrically connected to the negative electrode terminal laminated with a separator interposed therebetween, a first and second auxiliary insulating sheets each having a substantially U-shaped cross-section in a surface in the same direction as a surface of the square battery can on which the positive electrode terminal and the negative electrode terminal are formed, and an insulating tape 10. The first and second auxiliary insulating sheets are arranged at opposite sides to sandwich the electrode assembly and connected by the insulating tape 10.