PURPOSE: To contact a treatment solution of uniform temperature to the material to be developed by a method wherein the treatment solution flowed in from the bottom side of a longitudinally slender aperture runs on the flow passage of the desired length and it overflows, thereby enabling to give a high circulating property on the processing surface of a sample.

CONSTITUTION: The developing solution, which is controlled at the prescribed temperature by a temperature regulating unit 2, passes a flow-in duct 4 from a developing solution reservoir 1 by the circulating function of a pump 3, it flows in the bottom part of a developing solution feeding part 7, passes through a filter 8, and it overflows from an aperture part 10. The developing solution is received by an overflow vessel 9, passes through a flow-out duct 5 connected to the bottom part of the vessel 9, and it is circulated to and withdrawn by the developing solution reservoir 1 as shown by the arrow in the diagram. The surface to be treated of the sample 11 is brought sufficiently to come in contact with the developing solution overflowed from the aperture part of the developing solution feeding part 7, and a sample supporting and driving part 12 is reciprocatingly moved horizontally in the direction crossing the long side of the aperture 10. As a result, the temperature and the concentration of the treatment solution on the surface of treatment of the sample can be made uniform.