1. A method of discriminating a sample for a sensor system which quantitates the concentration of a target substance contained in the sample by measuring electric current, said method comprising the steps of: using a ratio of a measured current value to a time-differential value of the current value as a discriminating parameter; defining a discrimination function for discriminating kinds of a plurality of objective samples using a plurality of said discriminating parameters, said discrimination function using said discriminating parameters as independent variables, and said independent variables being multiplied by respective constants which are different from one another; using a numeric value obtained by substituting the values of said discriminating parameters into said discrimination function, as a discriminating index; and discriminating the kind of any sample based on said discriminating index.