A chlorine dioxide production device 1 includes a diaphragm electrolytic cell 2 having an anode chamber 3 and a cathode chamber 5 and configured to effect an electrolytic treatment on anolyte solution containing chlorite supplied to the anode chamber 3 for generating chlorine dioxide, a flow path section C communicating the anode chamber 3 to the cathode chamber 5, a discharge section D communicating the cathode camber 5 to the outside, an aerating means 14 for supplying aeration gas to the anode chamber with allowing adjustment of its supply amount, and a neutralizing means 12 for supplying a neutralizing agent to at least one of the cathode chamber 5 and the discharge section D.