PURPOSE: To obtain a bleached cellulose having high crystallinity, low polymerization degree and narrow polymerization degree distribution by extracting a defibrated lignocellulose substance successively with water, an alcohol and a caustic alkali and bleaching the residual cellulosic substance.

CONSTITUTION: A defibrated lignocellulose substance 26 is loosely packed in a column 21, water 27, an alcohol (isopropanol, ethanol or methanol) 28, a solution 29 of a caustic alkali having a concentration of <2% and a bleaching agent 30 are supplied to the top of the column, and a water-soluble fraction (vanillin, syringaldehyde, furfuraldehyde, protein, acetic acid, glucuronic acid, xylose monomer and oligomer) 31, an alcohol-soluble fraction (vegetable oil and lignin) 32, a caustic alkali-soluble fraction (xylose oligomer having high polymerization degree and lignin/furfuraldehyde copolymer) 33 and a fraction 34 soluble in the bleaching agent are collected from the bottom of the column. The caustic alkali extraction may be carried out directly without using the alcohol extraction.