An ion removal system comprising: an electrolysis device configured to generate alkaline water and acid water by electrolysis; a hard water flow path connected to the electrolysis device to supply the electrolysis device with hard water; a first flow path and a second flow path through which the alkaline water and the acid water generated by the electrolysis device can alternately flow; a fine bubble generation device (10A, 10B) configured to generate and supply fine bubbles to the hard water flow path, the first flow path, or the second flow path so as to adsorb and remove metal ions in water by the fine bubbles generated; a controller; a first return flow path connected from the first flow path to the hard water flow path; a second return flow path connected from the second flow path to the hard water flow path; a first valve configured to switch between allowing and stopping of water flow from the first flow path to the first return flow path; and a second valve configured to switch between allowing and stopping of water flow from the second flow path to the second return flow path, wherein the controller controls the electrolysis device to perform a first mode in which the alkaline water is allowed to flow through the first flow path and the acid water is allowed to flow through the second flow path and a second mode in which the acid water is allowed to flow through the first flow path and the alkaline water is allowed to flow through the second flow path, and the controller controls the first and second valves (30, 34) to allow the water flow from the first flow path to the first return flow path with stopping the water flow from the second flow path to the second return flow path in the first mode, and to stop the water flow from the first flow path to the first return flow path with allowing the water flow from the second flow path to the second return flow path in the second mode. an electrolysis device configured to generate alkaline water and acid water by electrolysis; a hard water flow path connected to the electrolysis device to supply the electrolysis device with hard water; a first flow path and a second flow path through which the alkaline water and the acid water generated by the electrolysis device can alternately flow; a fine bubble generation device (10A, 10B) configured to generate and supply fine bubbles to the hard water flow path, the first flow path, or the second flow path so as to adsorb and remove metal ions in water by the fine bubbles generated; a controller; a first return flow path connected from the first flow path to the hard water flow path; a second return flow path connected from the second flow path to the hard water flow path; a first valve configured to switch between allowing and stopping of water flow from the first flow path to the first return flow path; and a second valve configured to switch between allowing and stopping of water flow from the second flow path to the second return flow path, wherein the controller controls the electrolysis device to perform a first mode in which the alkaline water is allowed to flow through the first flow path and the acid water is allowed to flow through the second flow path and a second mode in which the acid water is allowed to flow through the first flow path and the alkaline water is allowed to flow through the second flow path, and the controller controls the first and second valves (30, 34) to allow the water flow from the first flow path to the first return flow path with stopping the water flow from the second flow path to the second return flow path in the first mode, and to stop the water flow from the first flow path to the first return flow path with allowing the water flow from the second flow path to the second return flow path in the second mode.