PURPOSE: To surely produce epoxy resin having α-glycol group of prescribed content related to the addition amount of glycidol.

CONSTITUTION: This epoxy resin is produced by adding glycidol of 0.0085 mol per hydroxyl equivalent of compound A, preferably at least 0.017 mol per hydroxyl equivalent in terms of 3-chloro-1,2-propanediol, during reaction of phenolic compound A having 2-4 phenolic hydroxyl group with epihalohydrin unsubstituted or substituted in 2- or 3-position with 1-4C alkyl. Preferably, sodium hydroxide, sodium methylate, quaternary phosphonium salt, ammonium salt, particularly 2-phenylimidazole is used as catalyst. The reaction is carried out at 20-200°C, particularly 40-120°C.