[PROBLEMS] To provide a blood dialysis apparatus and a method of examining a leakage therein whereby it is possible to avoid the application of an excessive load on a filter membrane of a filtration unit in examining a leakage in the filtration unit and to judge the occurrence of a leakage within a short period of time. [MEANS FOR SOLVING PROBLEMS] A blood dialysis apparatus comprising: a dialysis liquid-supplying line (L1) through which a dialysis liquid is supplied into a dialyzer (6) a dialysis liquid-discharging line (L2) through which the dialysis liquid is discharged from the dialyzer (6) a primary chamber (1b) in which the unfiltered dialysis liquid flows and a secondary chamber (1c) in which the filtered dialysis liquid flows that are partitioned with a filtration membrane (1a) a microparticle-filtering filter (1) for filtering and purifying the dialysis liquid flowing in the dialysis liquid-supplying line (L1) and an air-supplying unit whereby air can be supplied into the microparticle-filtering filter (1) during the leakage examination, which is further provided with an air detection unit (2) whereby air having been supplied from the air-supplying unit and passed through the filtration membrane (1a) of the microparticle-filtering filter (1) can be detected.
