A dialysis device 1 includes a water supply passage 15 for supplying clean water to solution supply chambers 35a and 35b, and a waste solution passage for discharging a used dialysis solution from solution collection chambers 34a and 34b, and the water supply passage includes a concentrate solution pump 21 that supplies a dialysis concentrate solution from concentrate solution supply source 19. The concentrate solution pump is a piston pump 40 that moves a piston 42 up and down in a cylinder 41 to feed a solution, the piston pump is provided in the way of washing passage 26 provided between the water supply passage and the waste solution passage, and an open/close valve 27 that intermittently opens and closes is provided in the washing passage to flow the clean water in the water supply passage through a gap between the cylinder and the piston.