A substrate treatment apparatus which can more efficiently regenerate phosphoric acid which is able to be returned to etching treatment along with such etching treatment as much as possible without using a large facility, that is a substrate treatment apparatus which treats a silicon substrate W on which a nitride film is formed by a liquid etchant which contains phosphoric acid, which comprises an etching treatment unit (the spin treatment unit 30) which gives a suitable quantity of liquid, etchant to each substrate which is fed one at a time so as to etch the substrate and remove the nitride film, a phosphoric acid regenerating unit (the spin treatment unit 30) which mixes liquid etchant used for treatment of one substrate and a suitable quantity of liquid hydrofluoric acid for the amount of the used liquid etchant under a predetermined temperature environment to regenerate the phosphoric acid, and a phosphoric acid recovery unit (the pump 38, phosphoric acid recovery tank 50, and pump 52) which returns the phosphoric acid which was obtained by the phosphoric acid regenerating unit to the liquid etchant to be used at the etching treatment unit.