A dialyzer (15) includes a hollow fiber dialysis column (20), a liquid tubing section (12a), and a flow rate changing section (16a). The hollow fiber dialysis column (20) includes a hollow fiber membrane, a first flow channel that allows a dialysis target to flow internally of the hollow fiber membrane, and a second flow channel that allows an external liquid to flow externally of the hollow fiber membrane. The liquid tubing section (12a) tubes the dialysis target to an inlet (20a) of the first flow channel. The flow rate changing section (16a) is capable of changing a flow rate of the dialysis target at the dialysis target flowing out of an outlet (20b) of the first flow channel.
