PURPOSE: To obtain high quality glassy carbon having high specular property of the polished surface and superior usefulness as a substrate for a magnetic recording medium by producing a glassy resin using a polyaddition- noncondensation type curing reactive resin as starting material.

CONSTITUTION: A polyaddition-noncondensation type curing reactive resin is used as starting material. It is preferable that the resin gives ≥40%, especially ≥55% yield of carbonization when the resin is carbonized by heating in an inert atmosphere. The resin preferably has one or more among an epoxy group, a cyano group and a polymerizable unsatd. bond in one molecule and it is typified by polyurethane resin, polyurea resin, epoxy resin, acryloyl resin, polystyrene resin or bismaleimide resin.