To provide a naphthol resin having slightly-changed heat resistance after subjected to a thermal history and exhibiting low thermal expandability, and further realizing excellent solvent solubility.

The naphthol resin contains 15-35% of a trimer, which is a polycondensate of an α-naphthol compound, a β-naphthol compound and formaldehyde and is shown by formula (1) (wherein R¹ and R² are each a hydrogen atom, a 1C-4C hydrocarbon group or a 1C-4C alkoxy group independently), and 1-25% of a dimer of the polycondensate.