Simultaneous measurement of impedance and turbidity changes in culture medium was proposed. The impedance change was measured by means of a four-electrode method. Two characteristic parameters for Escherichia coli and Staphylococcus epidermidis grown in Brain Heart Infusion broth were obtained. The growth speed α (inverse of generation time) and the delay time T of impedance change were computed as characteristic parameters from measured quantities. Since bacteria had inherent α and T, they were tentatively represented in term of a characteristic vector with two components α and T. Two bacteria were clearly discriminated on the two dimensional space.