A method and an apparatus for manufacturing trichlorosilane are disclosed. A polymer containing high boiling chlorosilane compounds that are generated in a polycrystalline silicon manufacturing process are mixed with hydrogen chloride and introduced into a decomposition furnace. The polymer and the hydrogen chloride are reacted at a temperature of 450° C., and preferably of 450° C. or more and 700° C. or less. Preferably a mixture containing the polymer and hydrogen chloride of 10 to 30 mass % with respect to the weight of the polymer is introduced into the decomposition furnace.