A gas cutting method for cutting a steel material and a steel material producing method including arranging one steel material and another steel material in proximity, setting a preheating region on the one steel material in such a way that a preheating flame applied thereto does not reach the other steel material, preheating the one steel material by applying the preheating flame to the preheating region, and gas-cutting the one steel material by moving a cutting oxygen from the preheating region across a boundary between the one steel material and the other steel material until the cutting oxygen enters the other steel material. The preheating region may be set in such a way that an outer edge of the preheating flame is at least 2 mm away from the other steel material.

A rolled steel bar for machine structural use includes a predetermined chemical composition. In the rolled steel bar for machine structural use, K1 obtained from K1=C+Si/7+Mn/5+1.54V is 0.95 to 1.05, K2 obtained from K2=13928.6Si+105Mn833S13420N is more than 35, a Mn content and a S content satisfy Mn/S8.0, and a total decarburized depth of a surface layer is 500 m or less.