Positive and negative electrodes include exposed current collector portions at both lengthwise ends, and these exposed current collector portions are bent such as to protrude from the widthwise edge of the electrodes to form welding pieces. The positive and negative electrodes and a separator interposed therebetween are wound around into a flat shape having an ellipsoidal cross section. The welding pieces of the positive and negative electrodes protruding from opposite sides of the wound electrodes are welded together with respective leads. According to this configuration, a simple but high-quality current collector design capable of stable electrical connection in a high power output prismatic electrochemical element is provided.