To provide a manufacturing method of modified novolac resin causing no gas generation in curing, with cured product having a very light-colored shade, and to provide the modified novolac resin.

There is provided a manufacturing method of modified novolac resin, wherein an addition reaction of a glycidyl acrylate and/or a glycidyl methacrylate with a nitrogen-containing resin. The nitrogen-containing resin has a structure of alternately repeating, via a methylene bond, an ethylene urea or a propylene urea and a hydroxy group-containing aromatic hydrocarbon having at least one hydroxy group as a substituent. The modified novolac resin obtained by the manufacturing method is also provided.