Method for manufacturing vehicle structural member

The present invention enables a vehicle structural member having a section where the width dimension is relatively narrow to be suitably manufactured using a hollow extrusion member. The vehicle structural member is manufactured by extruding and moulding a hollow extrusion member (50) in which an upper connecting plate (26), a lower connecting plate (28), and ribs (30, 32), which connect an outer-side plate (22) and an inner-side plate (24), each have a bent shape. At both end sections of the hollow extrusion member (50) in the longitudinal direction, the outer-side plate (22) is partially spaced away from the inner-side plate (24), and the width is increased to a width dimension (W2) so as to extend and flatten the upper connecting plate (26), the lower connecting plate (28), and the ribs (30, 32). Thus, even a vehicle bumper reinforcement (10) in which a width dimension (W1) of a narrow portion is relatively small can be suitably manufactured while minimising cracks, damage, and the like using the hollow extrusion member (50). Furthermore, the width is increased to the width dimension (W2) by pressing the outer-side plate (22) to a moulding surface (68) of a die (62), and the widened shape can therefore be precisely set with high accuracy by the moulding surface (68).