In cleaning the dialysis device, first, the concentrate passage is disconnected from the dialysis solution concentrate container and is connected to the branched passage, and a pre-cleaning process is performed in which the fluid circuit is replace with the purified water, and determining means (4a) of a control device (4) determines that the fluid circulating in the fluid circuit is not the dialysis solution by using a conductivity meter (29), and also determines that gas is not contained in the fluid circuit by using a downward movement detecting sensor 34b in a deaeration tank, and then a main cleaning process is performed by using a cleaning solution. Incomplete cleaning due to incomplete connection can be prevented.