PURPOSE: To shorten treatment time and to enhance the recovery rate of purified phosphorus by once introducing the whole quantity of the necessary quantity of nitric acid and crude phosphorus into a vessel, agitating and mixing the mixture in a short time.

CONSTITUTION: An agitation vessel is equipped with a cooling jacket 10 in the outer circumference of the vessel and also with a cooling pipe 20 and impellers 50 in the central part of the vessel and with baffle plates 5 in the side part. This agitation vessel is used and crude phosphorus (yellow phosphorus) and concentrated nitric acid are introduced into the agitation vessel. When the mixture is heated at melting point or more of phosphorus and phosphorus is melted, liquid phosphorus and nitric acid are separated into two layers by difference of specific gravity (specific gravity of P is 1.8 and specific gravity of HNO3 is 1.0). Two layers are agitated and mixed to disperse the fine particles of phosphorus into nitric acid. As this phosphorus dispersed in nitric acid by this agitation, its contact area with nitric acid is increased. Arsenic contained in phosphorus is oxidized by nitric acid and eluted as arsenic acid. Further a part of phosphorus is dissolved into nitric acid as phosphoric acid. In this case, the temperature of the dispersion liquid is gradually raised, and therefore, while keeping the liquid temperature at 46-53°C with a cooler, the dispersion liquid is agitated and purification of phosphorus is performed.