Morespecifically, if the hemolytic-state erythrocyte number r exceeds a predetermined level, the calculated number r may be erroneous.Therefore, the area C is an area variably set from the inputting section 61 in consideration of the time-related change in the number of the hemolytic-state erythrocytes.The computing section 65 computes the ratio h of the hemolytic-state erythrocytes from h=r/(R+r)