Doping with suppressed filament deterioration can be performed even in the case of doping in various conditions with an ion doping apparatus having a filament. After ion doping is completed, supply of a material gas is stopped and hydrogen or a rare gas is kept to be supplied. After that, current of the filament is decreased and correspondingly, filament temperature is decreased. Accordingly, in decreasing the filament temperature, the material gas around the filament has been replaced with hydrogen or a rare gas.