PURPOSE: To provide a biochemical analyzing device capable of deciding whether an inspection-object contains an interference substance or not.

CONSTITUTION: A biochemical analyzing device measures the electrode potential of an inspection-object A and that of an internal standard liquid B containing the electrolyte of a specified concentration, alternately, by using an ion selective electrode 8 which selectively responds to an ion to be measured and a reference electrode 7. By collating the comparison result with the calibration curve indicating the changes of electrode potential against that of electrolyte concentration, the electrolyte concentration of the inspection-object A is analyzed. A discriminating device 14 which calculates the variation level of the electrode potential of the internal standard liquid B, measured before and after the measurement of the electrode potential of the inspection-object A, and compares the variation level with a specified level, and an output device 15 which outputs the comparison result are provided.