PROBLEM TO BE SOLVED: To enable early start of cleaning of the entire blood purification system including a plurality of blood purifiers.SOLUTION: A computer of an RO device 2 receives signals indicating that cleaning has been completed in blood purifiers 1A, 1B from the blood purifiers 1A, 1B, and starts cleaning of the entire blood purification system including cleaning of an A raw liquid supply device 3 and a B raw liquid supply device 4 when detecting the completion of cleaning of all the blood purifiers in the blood purification system.