PROBLEM TO BE SOLVED: To apply a multicomponent system to a lignin-containing material and effectively carry out the delignification treatment by compounding many components of an oxidoreductase, an oxidizing agent, a mediator and an oxygen active additive. SOLUTION: This multicomponent system is prepared by compounding an oxidoreductase such as a laccase with its oxidizing agent and a mediator selected from the group of an aliphatic, an alicyclic, a heterocyclic or an aromatic compound having at least one functional group such as N-hydroxy, oxime, nitroso, N-oxyl or N-oxy or the like without deactivating the oxidoreductase and further at least one oxygen active additive selected from the group of a hydrolase (EC 3.2.1) such as a xylanase, a mannase or a cellulase or the like. The prepared multicomponent system is applied to a lignin-containing material and the resultant material is regulated so as to provide 0.1-100 IU of the oxidoreductase based on 1 g of the dry weight of the material, 1-500 mmol/kg cellulose of the mediator and 0.01-1,000 IU/g cellulose of the hydrolase (EC 3.2.1). Thereby, the delignification treatment thereof is carried out.