To efficiently remove foreign matters such as metal fittings which are in fixed states to a waste wood when pulverizing a ligneous biomass such as a building waste material.

The system for producing fuel by carbonizing the ligneous biomass and pulverizing the product involves removing the foreign matters after carbonizing the ligneous biomass and pulverizing the product by using at least one of a wind power-type classifier, a gravity-type classifier and a centrifugation-type classifier. The ligneous biomass after the carbonization is very brittle, and the metal fittings attached by screwing or the like to the ligneous biomass such as the waste wood can be easily removed as the foreign matters. At least one of the wind power-type, gravity-type or centrifugation type classifier is preferably used as the foreign matter-removing apparatus because the foreign matter fixed to the waste wood is not always separated by a magnet because of, for example, being copper or a ceramic (pottery and tile).