Recovery and reuse method of the specific raw materials (MEK, methanol and calcium chloride) used in the production of an MEK-modified resorcinol-formalin resin is provided. Furthermore, it is an object to stabilize quality by controlling a calcium chloride concentration in the MEK-modified resin to 100 ppm or less by partially improving the production steps. In a water solvent, resorcinol, a recovered calcium chloride aqueous solution, and a recovered MEK are added and stirred to form a two-phase system, and after adding a hydrochloric acid catalyst, formalin is added dropwise to the reaction system to allow a liquid-liquid heterogeneous reaction to proceed. It is allowed to stand to separate into two layers, and after removing an aqueous layer (0), water is added to an MEK layer (0) to sufficiently wash with water. It is allowed to stand to separate into two layers, and the aqueous layer (1) is removed. This water washing operation is further conducted at least one time to remove the aqueous layer (2), thereby obtaining the MEK layer (2) containing an MEK-modified resorcinol-formalin resin. Water is added to this MEK layer, 1 to 30% aqueous ammonia is added, MEK is recovered by rectification, and this is reused as the recovered MEK. Furthermore, after adjusting a calcium chloride concentration in the aqueous layer obtained by removing methanol from the aqueous layer (0) by reduced-pressure distillation, the aqueous layer is again returned to the reaction system, and reused. By this closed system recycle production method, the process for producing an MEK-modified resorcinol-formalin resin, in which recovery and reuse of specific raw materials (methanol, calcium chloride and MEK) are carried out in parallel, finally obtains a resorcinol-formalin resin aqueous solution having a reaction product concentration of from 30 to 80%, moderate flowability with a pH of 6 to 10, a calcium chloride concentration of 100 ppm or less, a peak area corresponding to a resorcinol monomer of from 3 to 9% to the entire peak area obtained by gel permeation chromatography analysis, and a peak area corresponding to resorcinol pentanuclear or higher nuclear bodies of from 30 to 55% to the entire peak.