PURPOSE: To get etchant whose etching rate is stabilized at the early stage after dilution by giving ultrasonic vibration to the chemicals inside a mixing vessel, and supplying gas into the chemical.

CONSTITUTION: A circulation filtering means 14 comprises a pump, a pipe, etc., and removes the fine particles inside the mixing liquid, communicating with a mixing vessel 1, and also it agitates the liquid. An ultrasonics oscillating means 15 comprises an ultrasonics generator 15a, a vibrator 15b, etc., and the vibrator 15b is fixed to the bottom of the mixing vessel. A bubbling means 16 communicates with a gas supply means, and discharges gas into the mixing liquid 1 through many small holes. To dilute etchant by this device, respectively specified amounts of undiluted solution and pure water are put in a mixing vessel 11, and ultrasonics are applied to this, and also while bubbling gas, circulation filtering is continued for a specified time.