When a load facing to the rear of a vehicle body acts on a knuckle mounting portion of an arm main body of a suspension arm, if the line of action of the load deviates vertically relative to the cross-sectional center of the arm main body, a moment that vertically deforms the arm main body occurs. However, since there are provided a first inclined projecting portion that is formed so as to bulge upward in an end part on a first vehicle body mounting portion side of a first bottom wall portion and has a height that gradually decreases in going from a first upper wall portion toward the second upper wall portion, and a second inclined projecting portion that is formed so as to bulge upward in an end part on the first vehicle body mounting portion side of a second bottom wall portion and has a height that gradually decreases in going from a third upper wall portion toward the second upper wall portion, it is possible to enhance the rigidity without increasing the weight of the arm main body, thus preventing deformation of the arm main body due to the load.