To aim at carrying out separation removing of aluminum chloride efficiently out of gas containing chlorosilane generated by a chlorination reaction furnace, and to provide a filter apparatus for removing metallic silicon fine powder or the like for that, and an apparatus and a method of purifying chlorosilane in gas after passing through the filter apparatus.

The filter apparatus 2 is for removing dust in gas containing chlorosilane generated by a reaction of metallic silicon and hydrogen chloride, wherein a filter using fabric of polytetrafluoroethylene or a membrane-like filter 12 comprising polytetrafluoroethylene as a continuous porous body is formed in the inside of a casing 11 which makes gas containing chlorosilane pass through, and a casing heating means 17 heating a wall of the casing 11 is formed.