To conduct good reutilization at the time of reutilizing the heating medium of a heat exchanger for adjusting the plating soln. of an electroplating tank by detecting the infiltration of a plating soln. into the heating medium with high sensitivity.

Pure steam is supplied to a heat exchanger 6 as a heating medium from a feeder 7 and heat-exchanged with a plating soln. to be supplied to an electroplating tank 2. The conductivity of the heat-exchanged medium is measured by a conductometer 13 and inputted to a controller 22. When the conductivity is below the prest reference value, the infiltration of the plating soln. is denied, and the heating medium is stored in a cushion tank 16 through a solenoid valve 15. Meanwhile, when the conductivity exceeds the reference value, the infiltration of the plating soln. is affirmed, and the plating soln. is discharged into a waste tank 12 through a solenoid valve 17. When the value detected by a level gage 23 for detecting the heating medium level in the cushion tank 16 exceeds the allowable minimum value, the medium is supplied to a main cleaning material feed pipeline by a motor-driven pump 18, and the set value of a flow control valve 21 is decreased in proportion to the supply.