Effective fillability and the uniformity electrodeposition of a copper electroplating solution is judged by determining the time-dependent potential change thereof at a cathode current density of 0.1-20 A/dm2. The potential change is determined at a working electrode rotation of 100-7500 rpm, and the fillability with the solution is judged from the curve profile. In an embodiment of the present invention, the fillability is judged by obtaining the potential change speed in the initial stage of electrolysis and the potential convergent point from the time-dependent potential change curve for a predetermined period of time after the start of the electrolysis.