Process for producing a valve metal powder by producing a precursor of desired morphology, converting the precursor into an oxide of the valve metal, stabilizing the structure of the oxide by heat treatment and reducing the stabilized oxide while retaining the morphology. A linking element has a first end operably connected to the valve and a second end. The corrected patch image is obtained through correction in accordance with the stepwise change of the rotation speed to be the same as the patch image formed when the rotation speed is not changed.