A heat exchanger includes an electrolytic bath and a control section. The electrolytic bath has first and second channels. A first fluid can flow through the first channel. A second fluid adapted to exchange heat with the first fluid can flow through the second channel. At least part of the first and second channels of the electrolytic bath is partitioned by anode and cathode plates to which a given potential is applied from a power source. The control section applies the given potential to the anode and cathode plates and performs polarity reversal adapted to reverse the polarity of the anode and cathode plates after having applied the given potential at given time intervals.