The present invention provides a method for casting a slab having a good cast surface. The method includes heating the surface of molten metal on a metal inlet side of a mold by a first heat source so that the following formulas: q≥0.87 and c≤11.762q+0.3095 are satisfied where c is a cycle time [sec] of turning movement of the first heat source, and q is an average amount of heat input [MW/m2] determined by accumulating an amount of heat input applied by at least the first heat source to the contact region between the upper surface of the slab on the metal inlet side and the mold, along the path of turning movement of the first heat source, and dividing the resultant accumulated value by the cycle time c.