PURPOSE: To uniformly distribute cashew dust in a friction material structure and prevent the generation of an abnormal sound by adding a foaming agent to the shell liquid of cashew nuts and pulverizing a foamed solid object obtained by reactional hardening and providing indefinite form of projecting edges on the surface of the foamed body structure.

CONSTITUTION: A cashew nut shell liquid 100 part is subjected to polymerization reaction in a reaction can and cooled and, then, a surface active agent and a foaming agent are added to it and mixed. The mixed liquid is poured into a kneader and, by adding hexamethylenetetramine, this mixed liquid is thinly applied to a pad, and heated and reactionally hardened and, after being cooled, the product is pulverized to obtain a cashew dust. Accordingly, the distribution of the cashew dust in a friction material structure can be made uniform, improving wear resistance and the stability of friction coefficient, while suppressing the generation of abnormal sound at the time of frictional action due to improved porosity.