PURPOSE: To avoid bad insulation by rolling and tightening an outer casing of a laminate with use of a press member having therein a circular-arc shaped peripheral groove of a specific cross-sectional configuration at the top end thereof circumferentially thereof.

CONSTITUTION: An outer casing 4 is formed by rendering a laminate to drawing and to blanking by a blanking device. The outer casing 4, after housing therein a capacitor element 5, is rolled and tightened along the opening end thereof by a press member 8. The press member 8 has at the circumferential top end a peripheral groove 7 of a specific cross-sectional configuration. The press member 8 is pushed down such that a deformation length of the outer casing in the rolling and tightening process from the opening end is 2.2 t1/2 (t: side wall thickness of the casing) or more. With respect to the cross-sectional configuration of the peripheral groove 7 in the press member 8 is defined such that the angle θ1 of the circular-arc from the deepest part 9 of the peripheral groove 7 toward the root of the press member is 80W90, and the radius of curvature R of the circular-arc is twice or more the side wall thickness of the outer casing. Hereby, a nylon resin layer 2 on an aluminum outer surface is allowed to cover the vertex ot the circular-arc, thereby assuring good insulation of the capacitor after being mounted.