In a purifying method for metal grade silicon, metal grade silicon with a silicon concentration not less than 98 wt % and not more than 99.9 wt % is prepared. The metal grade silicon contains aluminum not less than 1000 ppm and not more than 10000 ppm by weight. The metal grade silicon is heated at a temperature not less than 1500° C. and not more than 1600° C. in an inert atmosphere under pressure not less than 100 Pa and not more than 1000 Pa, and maintained at the temperature in the atmosphere for a predetermined period.