To provide a producing method of a member for motor car made of an aluminum alloy having high mechanical strength in the whole body and light weight.

In the producing method of the member for motor car, produced with a semi-solidified die casting method of Al-Si-Mg base alloy, the cross section of a cavity in a die for casting is formed so as to be at least almost U-shape, and the Al-Si-Mg base alloy in the semi-melting state is poured into the cavity and produced so that the matrix structure forms as substantially granular state.