PURPOSE: To eliminate auxiliary parts, such as a connecting tool and a clamping tool by composing a metal base material of one continuous substrate continuously bent in a wave shape.

CONSTITUTION: Electronic component group 3 is soldered to a metal base substrate before bending. Both ends are grasped by a movable clamp 7, and its center is clamped by a stationary clamp 6. The center between the clamps 6 and 7 is lifted vertically by cutting edges 4, 5, the clamp 7 is simultaneously moved horizontally to the clamp 6 at the same speed to form a wave shape. The clamps are removed to complete a bent metal base substrate 2b. Since auxiliary parts are not required, an effective mounting area is increased, and since a connector between the substrates is eliminated, its connecting reliability is enhanced.