The fulvic acid solution production method of the present invention comprises: an apparatus preparation step of preparing a processing apparatus which comprises: a hermetic container internally having a closeable processing space; a steam jetting device operable to jet high-temperature and high-pressure steam into the hermetic container; a supply section having an opening-closing mechanism and operable to supply a raw material into the hermetic container; and a discharge section having an opening-closing mechanism and operable to discharge, to the outside, a processed liquid produced through processing of the raw material by the steam; a raw material input step of inputting a raw material containing chips of wood as a primary raw material, from the supply section into the processing space of the hermetic container of the processing apparatus; a stream introduction step of introducing steam having a temperature of 120 to 250° C. and a pressure of 12 to 35 atm into the processing space in which the raw material is input; a processing step of subjecting the raw material to a subcritical water reaction processing, under stirring, while introducing the steam; a mixed solution obtaining step of cooling the processed raw material after the processing step to obtain a mixed solution containing fulvic acid and humic acid; and a fulvic acid solution taking-out step of separating humic acid and fulvic acid from the obtained mixed solution to take out a fulvic acid solution.