An improvement in cement used for mass concrete, high-strength concrete, high-fluidity concrete, noncontractive concrete and high-durability concrete in the fields of civil engineering and construction, and for building materials manufactured by extrusion molding and sheet making. When the ratio of A12O3 to Fe2O3 in the cement clinker is regulated to a value of 0.05-0.62, the strength of high-strength and high-fluidity concrete can be further improved, and the heat of hydration can be minimized as the fluidity improving performance and long term strength of the cement are maintained.