Technical indexes :

Type	F-51	F-44(644)	F-48(648)
Appearance	High viscosity brown clear liquid		Brown lump solid
Epoxide value (eq/100g)	≥0.50	0.40	0.44
Unhydrolytic chlorine (eq/100g)	≤0.005	0.005	0.005
Hydrolytic chlorine(eq/100g)	≤0.02	0.05	0.08
Volatile %	≤2	2	2
Softening point °C	≤28	40	70

The heat-resistant epoxy resin composition of claim 1 wherein the epoxy hardener is a novolak phenol resin, an aralkyl phenol resin or a polyhydric phenol. The epoxy resin is improved in adhesiveness and toughness when compared with the conventional highly heat-resistant epoxy resins.

Specifically disclosed is an epoxy resin obtained by glycidylation of a mixture of (a) a phenol condensation product which is a condensation product of a phenol and glyoxal and contains not less than 80% (area% determined by gel permeation chromatography) of a compound represented by the formula (1) below, and (b) a phenol other than the component (a) or a phenol resin. (1) (In the formula, R's independently represent a hydrogen atom, a hydrocarbon group having 1-15 carbon atoms or a trifluoromethyl group.)