A glucose sensor system comprising the steps of using as a sample discriminating parameter a ratio (I/.DELTA.I) of a measured current value I to the time-differential value of the current value .DELTA.I, defining a discrimination function that discriminates whether a sample is blood or control fluid and uses the discriminating parameter as an independent variable, quantitating as a discriminating index a numeric value obtained by substituting a discriminating parameter value into this discrimination function, and automatically discriminating, based on this index, whether the sample is blood or a control fluid, whereby a kind of the sample can be automatically quantitated by measuring electric current when a sensor system is used for quantitating the concentration of an analysis object in the sample.