An electrolyzed water generating device 1 has an electrolysis chamber 40, a first feeding body 41 and a second feeding body 41 to which a DC voltage is applied, a diaphragm 43 disposed between the first feeding body 41 and the second feeding body 42 to divide the electrolysis chamber 40 into a first-polar chamber 40a and a second-polar chamber 40b, a control unit 5 for switching a polarity of the first feeding body 41 to an anode or a cathode and a polarity of the second feeding body 42 to a cathode or an anode, a flow rate sensor 22 detecting an amount of flowing water into the electrolysis chamber 40 on the cathode side per unit time, and a current detecting means 44 detecting a DC current supplied to the first feeding body 41 and the second feeding body 42. The surfaces of the first feeding body 41 and the second feeding body 42 are formed of a hydrogen storage metal. The control unit 5 calculates a concentration of hydrogen storage metal colloid based on the DC current and an integrated value of the amount of flowing water after switching the polarities.