A controller C executes a first operation of operating a dialysate pump 27 at a predetermined set flow rate, to obtain total discharge time until dialysate supplied to fill a supply chamber 21a of a dialysate chamber 21 runs out. Next, the controller executes a second operation of operating a fluid replacement pump 19 at a predetermined set flow rate only for predetermined time, to discharge a part of the dialysate supplied to fill the supply chamber 21a, and next executes a third operation of operating the dialysate pump 27 at the same set flow rate as in the first operation again, to obtain remaining discharge time until residual dialysate remaining in the supply chamber runs out after the end of the second operation. A substantial flow rate of the fluid replacement pump can be calculated from the total discharge time and the remaining discharge time, and hence in a calibrating operation of the fluid replacement pump, the controller adjusts setting of the fluid replacement pump to eliminate a difference between the set flow rate and the substantial flow rate in the fluid replacement pump.The flow rate of the fluid replacement pump 19 can be calibrated without adding any special configuration.
