PURPOSE: To determine the quantity of each ion in residue highly accurately by extracting ionic residue into mixed solution, diluting the residue, and thereafter separating each ion.

CONSTITUTION: In an ultrasonic-wave extracting tank 31, ultrasonic wave are applied on electronic parts in mixed solvent of alcohol and water. Ionic residue on the surface of the part is extracted into the mixed solvent. A dilution adjusting device 42 dilutes the mixed solvent wherein the ionic residue is extracted into the specified concentration of alcohol. An ion determining device 33 separates the ionic residue in the diluted mixed solvent and determines the quantity by ion chromatography. The device 33 separates the ion component in the extracted liquid with an ion exchange resin column and detects the electric conductivity in proportion to the concentration of the ions. Standard liquid containing ion species to be determined is measured, and a calibration curve showing the relation between peak intensity and ion concentration is formed beforehand. Thus the highly accurate determination can be performed.