To especially improve mechanical properties in a resin composition in which polyacetal-based resin is mixed with a surface-treated functional inorganic filler.

The polyacetal-based resin composition is obtained by adding 20-25 pts. wt. inorganic filler surface-treated with 0.5-3.0 wt.% of an alkoxysilane having at least one amino group in the molecule, e.g. 3-aminopropyltriethoxysilane to 100 pts. wt. polyacetal-based resin. The alkoxysilane which is a surface treating agent has good bonding property to the inorganic filler and it is thought that the alkoxysilane has excellent compatibility with the polyacetal-based resin. As a result, remarkable improvement of physical properties of the molded product is obtained.