To prevent scale from being adhered to the surface of an aluminum electrode even if an electrical energization at the aluminum electrode within a filtering tank is repeated, and to cause scales or germs accumulated within a bathtub to be coagulated and removed.
A specified current is applied to an aluminum electrode 26, its electrical energization time is stored and when an accumulated electrical energization time becomes a specified value, a display of cleaning is carried out at an external input device. Then, a user carries out a cleaning operation; same scales at the surface of the aluminum electrode 26 are removed. Thus, either some scales or germs accumulated within the bathtub can be coagulated and the coagulated foreign substances can be removed through a filtering material 25 within the bathtub, resulting in that even if several persons take a bath in a continuous manner, water in the bathtub can always be kept clean and sanitary state.
SONEDAKA KAZUNORI
AOKI TETSUO
UEHARA KAZUHITO
