To efficiently and stably reduce scale flaw generated in hot rolling process for a steel containing ≥0.01% Ni, Cu.

A steel containing, by mass %, ≥0.01% Ni+Cu and ≤0.25% Si is heated in oxidizing atmosphere and is subjected to hot rolling after descaling. As an index to quantify scale matrix iron boundary property after heating/ before hot rolling, a line segment of 300μm length, which is a basis for observation range in the direction orthogonal to the vertical direction on the cross section of vertical direction for steel surface after heating, is set as shown in the figure, a ratio L/A of a boundary length L measured along the boundary of scale matrix iron boundary in the observation range sandwiched with two lines passing both ends P, Q and parallel to the vertical direction and a straight line length A of the line segment is obtained. by adopting the average values at least arbitrary three places, a steel is heated so as to have the average values of ≤1.70.