PURPOSE: To make it possible to treat a patient by deciding the pathological state with accurately by checking a pathological state chart and normal value range on the whole by drawing the loci of the least upper bound and greatest lower bound on a pathological state chart.

CONSTITUTION: With the automatic switch of key switch 5 depressed, microcomputer μCM1 reads the least upper bound values and greatest lower bound values of respective data, such as blood-oxygen partial pressure PaO2, blood-carbon-dioxide partial pressure PaCO2, bloold-ion concentration pH, and blood-bicarbonate-ion concentration HCO3, stored in the memory and voltage drawing respective loci are output from DA converters 25W28 and then input to the X axis and Y axis of CRT6 by way of X-axial and Y-axial multiplexers MPX3 and MPX4. On CRT6, loci A and B of the least upper bound value and greatest lower bound value of each data are displayed. Next, when four data are input by pushing keys of switch 5 that correspond to data items, μCM1 outputs voltages of data loci to DA converters 29 and 210 and locus D of the data is displayed on CRT by way of MPXs 3 and 4.