To obtain an epoxy resin excellent in reactivity, hardly causing blocking during storage, useful as an adhesive, etc., by specifying an epoxy equivalent and a hydrolyzable chlorine amount.

This epoxy resin of formula I ((n) is an average value and is a positive number of 0 to 1; G is glycidyl) has ≤190g/eq epoxy equivalent and ≤500ppm hydrolyzable chlorine amount. The epoxy resin is obtained, for example, by reacting a dissolved mixture of a compound of formula II, an excessive amount of an epihalohydrin such as epichlorohydrin or epibromohydrin and an aprotic polar solvent at 20-120°C for 0.5-10 hours by adding an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide.