Colored wastewater from industries, agriculture and the like is discolored by adjusting pH of the wastewater and filtering the wastewater through a mixture of acid-treated sawdust produced from sawdust which has been disposed of after being used for fungi production and charcoal thereby to remove a color component fraction from the wastewater and through a filter material, for example acid-treated rice husk charcoal, in which autochthonous microorganisms are embedded thereby to absorb color components remaining in the wastewater.