PURPOSE: To provide a rain gutter such as an elbow having a large curvature without water leakage by forming a pair of channels having a curved groove line by drawing of a flat metallic sheet then superposing the channels to a curved cylindrical shape having the curved axial line and welding the superposed parts.

CONSTITUTION: A flat metallic sheet 1 is formed by drawing to an approximately sectionally U-shaped channel 2 having a groove line L curved approximately to an L shape. The channels 2 formed symmetrically with each other are superposed to a cylindrical shape having the curved axial line L' and the superposed parts 3 constituted by collar parts 6 are tightly adhered by arc welding or beam welding using a welding rod in a way as to avoid water leakage, by which an elbow 8 is manufactured.