First, thanks for the answers.

I can remove those wierd patterns by increasing the ray bias,
but it makes less reflection as bagginsbill said.

Since I'm really newbie to this 3D things, I cannot understand something like "tripling bad polys" now.
I think I have to give up this car (because other one does not makes problem at all),
and have other trials using poser.

I really appreciate to all your helps.
Thanks.