A process for concentrating and recovering a surfactant aqueous solution, by evaporating and concentrating a surfactant aqueous solution containing a gasifiable surfactant and an aqueous solvent to increase the concentration of the surfactant, which comprises: storing the surfactant aqueous solution in an evaporator; adjusting the temperature of the surfactant aqueous solution in the evaporator to be lower than the boiling point of the aqueous solvent under the pressure in the evaporator; withdrawing a part of the surfactant aqueous solution from the evaporator, superheating it in a superheater under conditions that all the surfactant and the aqueous solvent are formed into an annular flow or an annular mist flow, once pressure-condensing the surfactant aqueous solution in a nozzle and spraying it into the evaporator by the nozzle having a shape such that the outlet side first narrows and then widens outward; and evaporating and removing the aqueous solvent, wherein the superheater and an upper portion of the evaporator are connected by a piping. wherein the superheating of the surfactant aqueous solution in the superheater is carried out to satisfy the conditions of the following formulae and calculated from "Transition formula of the liquid-vapor two phase flow in vertical piping", u G > Ku G 0.2 × Fr G 0.36 1.9 8 × u L u L < ρ L − ρ G × d × g 2 × f L × ρ L 0.5 × 1.7 σ ρ L − ρ G × g × d 2 − 0.25 in the above formulae, u represents the gas superficial velocity (m/s) in the piping, u the liquid superficial velocity (m/s) in the piping, Ku the Kutdelaze number, Fr the Froude number, ρ L the liquid density (kg/m 3) of the surfactant aqueous solution, ρ G the gas density (kg/m 3) of gas obtained by vaporizing the surfactant aqueous solution, d the inner diameter (m) of the piping on the upstream side of the nozzle, g the gravitational acceleration (m/s 2), and σ the surface tension (N/m) of the surfactant aqueous solution, further, f L is the coefficient of friction, and is f L =16/Re in the case of the laminar flow and f L =0.079×Re -1/4 (wherein Re is the Reynolds number) in the case of the turbulent flow, and wherein the nozzle has a pressurizing portion where the inner diameter of the flow path gradually decreases, an open portion where the inner diameter of the flow path gradually increases, and a connecting portion having a constant inner diameter of the flow path, connecting the pressurizing portion and the open portion, wherein the angle at which the inner wall opens at the open portion of the nozzle is from 90 to 180°. storing the surfactant aqueous solution in an evaporator; adjusting the temperature of the surfactant aqueous solution in the evaporator to be lower than the boiling point of the aqueous solvent under the pressure in the evaporator; withdrawing a part of the surfactant aqueous solution from the evaporator, superheating it in a superheater under conditions that all the surfactant and the aqueous solvent are formed into an annular flow or an annular mist flow, once pressure-condensing the surfactant aqueous solution in a nozzle and spraying it into the evaporator by the nozzle having a shape such that the outlet side first narrows and then widens outward; and evaporating and removing the aqueous solvent, wherein the superheater and an upper portion of the evaporator are connected by a piping. wherein the superheating of the surfactant aqueous solution in the superheater is carried out to satisfy the conditions of the following formulae and calculated from "Transition formula of the liquid-vapor two phase flow in vertical piping", u G > Ku G 0.2 × Fr G 0.36 1.9 8 × u L u L < ρ L − ρ G × d × g 2 × f L × ρ L 0.5 × 1.7 σ ρ L − ρ G × g × d 2 − 0.25 in the above formulae, u represents the gas superficial velocity (m/s) in the piping, u the liquid superficial velocity (m/s) in the piping, Ku the Kutdelaze number, Fr the Froude number, ρ L the liquid density (kg/m 3) of the surfactant aqueous solution, ρ G the gas density (kg/m 3) of gas obtained by vaporizing the surfactant aqueous solution, d the inner diameter (m) of the piping on the upstream side of the nozzle, g the gravitational acceleration (m/s 2), and σ the surface tension (N/m) of the surfactant aqueous solution, further, f L is the coefficient of friction, and is f L =16/Re in the case of the laminar flow and f L =0.079×Re -1/4 (wherein Re is the Reynolds number) in the case of the turbulent flow, and wherein the nozzle has a pressurizing portion where the inner diameter of the flow path gradually decreases, an open portion where the inner diameter of the flow path gradually increases, and a connecting portion having a constant inner diameter of the flow path, connecting the pressurizing portion and the open portion, wherein the angle at which the inner wall opens at the open portion of the nozzle is from 90 to 180°.