PURPOSE: To obtain cast iron excellent in weatherability and workability and having good castability at low cost by specifying the carbon saturation and the compsn. constituted of C, Si, Mn, S, P, Cr, Cu, Ni, Mg and Fe in the cast iron.

CONSTITUTION: This cast iron is one having carbon saturation Sc=C/(4.23-Si/3.2) in the range of 0.9 to 1.2, contg., by weight, 2.8 to 3.8% C, 2.6 to 3.8% Si, 0.01 to 0.6% Mn, ≤0.015% S, 0.05 to 0.3% P, 0.1 to 0.6% Cr, 0.2 to 2.0% Cu, 0.1 to 2.0% Ni and 0.003 to 0.060% Mg, furthermore contg., at need, one or more kinds of 0.0003 to 0.005% Bi and 0.0003 to 0.005% rare earth elements and the balance Fe with inevitable impurities, having preferably ≤5% areal ratio of carbides in the metallic structure and excellent in weatherability or the like. The cast iron is suitable as the one for building and for structural and design members.