PURPOSE: To enable the determination of the degree of stability of an electrolytic solution by agitation, by arranging first and second electrodes, a voltage application means, a measuring means, a cleaner and a driving means.

CONSTITUTION: When a switch 20 is closed, a DC voltage is applied between electrodes 10 and 12, but as phosphor particles are charged positively by aluminum ions Al3+ in an electrolytic solution 100, they deposit to the cylindrical negative electrode 12. Therefore, with the rotation of the electrode 12, a cleaner 16 slides in friction on the circumferential surface of the electrode 12 to remove the deposited phosphor particles from the electrode 12. The current (i) flowing between the electrodes 10 and 12 runs through a resistance 22 to generate a voltage iR, which is measured with a voltmeter 24 and hence, the current (i) can be determined as i=V/R from the voltage value V with the voltmeter 24. Thus the degree of stability of the electrolytic solution can be determined by measuring the current flowing between electrodes while stirring up the solution.