An electrolysis device, for producing alkaline water from water, includes an electrolysis vessel, a pair of high porous electrodes arranged in the electrolysis vessel, and a cell unit arranged between the positive and negative electrodes. The pair of high porous electrodes respectively serve as a positive electrode and a negative electrode. The cell unit includes a bipolar membrane element and at least one cation exchangeable membrane. The bipolar membrane element has a cation exchangeable side and an anion exchangeable side. The cation exchangeable side is closer to the negative electrode than the anion exchangeable side. The cation exchangeable membrane is arranged between the anion exchangeable side of the bipolar membrane element and the positive electrode, so as to define an alkalic chamber between the bipolar membrane element and the cation exchangeable membrane.