PURPOSE: To obtain the subject filler having high abrasion resistance and excellent stability of frictional coefficient and useful as an additive for a friction material such as brake shoe by swelling a highly water-absorbing resin with water in advance and dispersing the resin in cashew dust.

CONSTITUTION: The objection filler is produced by swelling a highly water- absorbing resin (e.g., crosslinked polyacrylic acid resin, isobutylene/maleic acid resin or PVA/polyacrylic acid salt resin) with water in advance and dispersing the soaked resin in cashew dust. Preferably, the highly water-absorbing resin is mixed in the cashew polymer, the compounded components are hardened by reaction and the reaction product is crushed and moistened to obtain the objective filler.