PURPOSE: To reliably conduct an optimum treatment in an efficient manner by a method wherein the current flowing in the electric circuit, formed between the chuck member supporting a substrate and a flow-out means through the intermediary of a treatment solution, is detected and the condition of etching and developing is automatically detected.

CONSTITUTION: A chuck 11 pinches a substrate 1 from the side face of the substrate, and it becomes the first electrode by contacting to the Al layer on the substrate. The container 12a as an etchant continuously flowing means is different from an Al layer 7, and a metal (a platinum wire, for example) 13 which becomes the second electrode is housed therein. An electric current is formed by the substrate 1, the chuck 11, a lead wire 15, the platinum wire 13 in the container 12a, and an etchant 10 flowing down from the container 12a. By the battery action generated by chemical change, a current is made to flow with the platinum wire 13 as a plus pole and the Al layer as a minus pole. The end point of etching is detected by measuring this current. As a result, an optimum treatment can be conducted reliably and efficiently.