To omit the updating of a calibration curve and to suppress the consumption quantity of a reagent for calibration when the reliability of an electrode and a device is secured in a stable state by judging calibration implementation propriety before calibration is actually made.

When the electrolyte concentration in a specimen is automatically measured by an ion selective electrode provided on the measurement section 15 of a clinical electrolyte concentration analyzer in this measuring method, a CPU 20 measures specific samples (blood serum low concentration calibrated liquid, blood serum high concentration calibrated liquid, urine low concentration calibrated liquid, urine high concentration calibrated liquid) with a calibration curve and judges whether calibration should be made or not this time based on the obtained measurement values.