A dialysis device 1 includes a fluid circuit 2 including a water supply passage 12 for supplying purified water to a measuring chamber 11, concentrate passages 13A and 13B which join the purified water passage and are connected to dialysis solution concentrate containers 20A and 20B respectively, a branched passage 14 branched from the purified water passage, cleaning solution passage 15 for circulating a cleaning solution through the branched passage, a conductivity meter 29 as a dialysis solution detector, and a deaeration tank 34 as a gas detector. 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, 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.