To obtain a trifunctional epoxy resin which can give cured products having a Tg of 200°C or above, low water absorptivity, good flame retardancy and high hardness and shows melt processability useful for lamination, molding and/or compositing by using a trifunctional epoxy resin having a specified structural formula.

This resin has a structure represented by formula I (wherein R1 and R6, which are independent of each other, are hydrogen atoms or 1-20C alkyls, and when the two R1s are not hydrogen atoms simultaneously, then R2 is combined with the methyl group or R3 to form a fused ring, and R4 and R5, which are independent of each other, are 1-6C alkyl groups or are combined with each other to form a spiro ring). The trifunctional epoxy resins are desirably those having structural formulas II and/or III.