PURPOSE: To automatically determine the sensitivity curve of a photoresist in a short period by developing a wafer which is continuously changed in the exposure under specified conditions, scanning the laser light and continuously measuring the interference light from the photoresist.

CONSTITUTION: The wafer 10 on which the photoresist is coated is disposed in an exposing region S and the full surface exposing to the photoresist is started. The wafer is moved from the exposing region to the outside of the exposing region in such a manner that the exposure changes continuously. Such wafer is developed under the specified conditions and the laser light of a film thickness detector 11 is scanned along the direction where the exposure of the photoresist changes continuously. The interference light from the photoresist is continuously measured and the sensitivity curve of the photoresist is determined in accordance with the measurement data. The sensitivity curve of the photoresist is thereby automatically determined in a short period.