PURPOSE: To always enable the constant development of the titled photoresist, even in the case of change in the composition of a developer by finishing the development at the time when the extinction of the developer is increased by a prescribed amount, by dissolving a photoresist in the developer.

CONSTITUTION: The developing tank 1 is constituted of a light shielding material, and a cell 8 protruding to out side is provided at a part of said tank, and a spectrophotometer 9 capable of detecting the extinction of the developer 2 is provided within the cell 8. When the photoresist is dipped in the developer 2, and the extinction of the developer 2 which changes due to the dissolution of the photoresist increases to the prescribed value, the development of the objective material 5 to be developed, is finished.