[Objects] To improve productivity and reduce thermal energy consumption in manufacturing of high purity silicon as a raw material for metallurgical grade pure silicon.[Means to Solve]After conducting a first treatment of either removing boron by water-vapor added plasma arc heating or low-pressure oxygen plasma arc heating upon raw silicon contained in a hearth in a chamber to thereby putting the raw silicon into a high temperature molten state to thereby oxidizing and removing boron by evaporation, or removing phosphorus by electron beam irradiation to thereby putting the raw silicon into a high temperature molten state to thereby remove phosphorus by evaporation in an atmosphere suitable to the treatment; the atmosphere of the chamber is then changed to a vacuum atmosphere suitable to the remaining second treatment, while maintaining the silicon contained in the hearth in its molten state, and the second purification treatment is conducted; whereafter end(s) enriched in impurities is cut off by way of one-way coagulation method to obtain a high purity refined silicon ingot highly free from phosphorus, boron and other impurities.