To provide a production method which enables to easily obtain a synthetic resin filler or a cellulosic carbonized material from a lignocellulose resource at a low cost.

The method for producing a synthetic resin filler includes: a steam distillation step of subjecting a lignocellulose resource to steam distillation treatment; a pulverization step of pulverizing a treated material subjected to steam distillation treatment; a fine powdering step of reducing a pulverized material obtained in the pulverization step to a fine powder; and a superheated steam treatment step of subjecting the fine power obtained in the fine powdering step to superheated steam treatment at a temperature of 150-250°C. The method for producing a cellulosic carbonized material includes a heat treatment step of heat-treating the fine powder at a temperature of 200-400°C.