PURPOSE: To obtain efficiently a low P steel by carrying out primary blowing using pig iron contg. C and P as a principal starting material and steel making slag produced in a refining furnace as a slag forming agent and carring out secondary blowing.

CONSTITUTION: Primary blowing is carried out using pig iron contg. at least C and P as a principal starting material and steel making slag produced after refining in a refining furnace such as a converter as a slag forming agent. The percentage of the slag is adjusted to ≥ about 10%. Secondary blowing is then carried out by a conventional method, and the resulting steel is discharged. The P concn. of the steel can be reduced to ≤ about 0.005%.