To provide a hot-rolled flat steel bar in which the surface skin is adequately bright and adequately dim, and capable of demonstrating a novel design effect, and its manufacturing method.

The hot-rolled flat steel bar comprises austenitic steel having a surface layer part of a passive film, and has the skin gloss having excellent design property. Glossiness on the surface of the surface layer part is 5-20 in terms of the glossiness specified in JIS Z8741, the Vickers hardness (Hv) of a portion to the depth of 0.05 mm from the surface of the surface layer part is ≥250, and the permeability is ≤1.02.