To provide a spoiler for an automobile wherein a number of part items is decreased, a cost of manufacture can be reduced, and lighting of weight and improvement of rigidity can be attained by gas assist injection molding method.

A spoiler 1, formed in almost rectangular shape as viewed by plane, is shaped so as to open a lower surface side, from a peripheral edge of an upper surface part 1a, a front end flange part 1b, rear end flange part 1c and side end flange parts 1d, 1d are respectively hung down, and a connection piece 1e partially connecting the fellow both end flange parts 1b, 1c is provided. In the case of molding the spoiler 1 by gas assist injection molding method, a gate 2 for injecting gas in a cavity is positioned in the vicinity of the connection piece 1e, and just after completion with an injection charge in a metal mold cavity of resin, when gas is injected in the cavity from a part of the gate 2, the gas passes through a part of the connection piece 1e to be introduced in a part of the rear end flange part 1c. In a part of the front/rear end flange part 1b, 1e, hollow gas channels 1f, 1f are respectively formed.