To produce a widely usable carbonization product while effectively utilizing waste culture media which are now occurring in a large amt. since mushrooms, etc., are now cultivated on a large scale and which can not be totally consumed by using only as fertilizer or feed and are beginning to be treated as an industrial waste.

This carbonization product comprises a particulate carbonization product 2 obtd. from waste culture media contg. corn cob and a starch paste 3 binding particles of the particulate carbonization product, is porous because of microvoids 4 formed by the bound particles of the particulate carbonization product, and is produced by a process comprising the step of drying waste culture media for mushroom cultivation, the step of carbonizing the dried waste culture media by baking, and the step of mixing the carbonization product with a binder and molding the resulting mixture in a mold.