PURPOSE: To remove developing unevenness, and simultaneously, to shorten developing time by rotating a board in a developer, and moving every part of the board close by an ultrasonic wave oscillator to ultrasonic-vibrate the developer.

CONSTITUTION: While the developer 6 is ultrasonic-vibrated by the ultrasonic wave oscillator 7 as swinging the board 1 immersed in the developer (pure water) 6 up and down and right and left, the board 1 held by a jig 5 is rotated, and the part of the board 1 positioned far away from the ultrasonic wave oscillator 7 is moved by turns to the vicinity of the ultrasonic wave oscillator 7. Thus, every part of the printed board 1 brought into contact uniformly with the developer 6 ultrasonic-vibrated by strong energy at the vicinity of the ultrasonic wave oscillator 7.