In color coating processes, a pre-treatment process is a one of most of essential operations to clean all dusts and grease out from product parts. A degreasing step in the pre-treatment process becomes more important recently. Even though monitoring cleanser concentration in a degreasing bath can be indicated by Phenolphthalein-alkalinity (P-alkalinity) titration, this procedure carried out by human leads to unsatisfactory error. Moreover, the control of concentration of the solution is very difficult. This