To obviate an installing space of a new resonance noise eliminator, to simplify a structure, and to reduce cost by communicating one of left/right side frames with an intake port of an engine, communicating the side frames with cross members, and constituting the cross members as a resonance noise eliminator.

Left/right side frames 1, 2 are constituted as a hollow member having a cross section of a rectangular shape, and one end side is used as an intake air passage of an engine. Plural cross members 6, 7 for connecting/ joining both are installed between these left/right side frames 1, 2. An intake air passage side end part of a front cross member 6 is constituted as an intake port 8 of air sucked in the engine, and the inside of the front cross member 6 becomes a blocking-up chamber communicated with the left side frame 1. When air passes by the action of this blocking-up chamber, the blocking-up part inside resonates to attenuate sound energy of a prescribed frequency to reduce an intake air sound of the engine.