PURPOSE: To provide the front side member of an automobile which prevents the resonance of a rigid part with the vibration having a relatively low frequency.

CONSTITUTION: The front side member of an automobile is equipped with a rigid part 20 which is formed to a closed section by an inner panel 24 and an outer panel 26 and extends in the longitudinal direction of a car body and a base part extending from the rigid part inward and downward in the horizontal direction of the car body. The rigid part 20 is arranged in a closed section, and is equipped with a reinforcement 28 extending in the longitudinal direction of the car body. The reinforcement 28 is made shorter than the outer panel 26 in an upper part 30, and is equipped with a rectilinear corner part 33. Accordingly, the axis line I1 which is one among the orthogonal coordinate axis lines as the main axis of the closed section and generates the max. sectional secondary moment is set inward and downward from the outside in the horizontal direction of a car body.