Rear arm for motorcycle

b b c c a a c c g g A rear arm for a motorcycle obtained by weld-bonding left and right arm molded bodies and made of aluminum alloy die-cast, which are formed by dividing pivot sections and and cross member sections and into left and right parts along a body central line, in the pivot sections and the cross member sections is provided, in which left and the right arm sections and are formed in substantially a triangular shape in side view and formed in substantially C shape opening toward an inner side in a width direction of the vehicle in cross-sectional view, and the cross member sections and are formed in a closed sectional shape extending from vertexes and of the triangular shapes to bases thereof.