A method for detecting and identifying a chemical substance in various phases such as a vapor phase and a liquid phase. The chemical substance being measured is diffused into a predetermined phase. Then, an electric state at an electrode existing in the predetermined phase is detected as a change with time based on the diffusion and absorption of the chemical substance on the electrode. A pattern of the change of the electric state with time is prepared. A fitting function based on the pattern is set and parameters of the chemical substance being measured are found. A distance between the parameters of the chemical substance being measured and parameters of the reference substance which is detected is determined. In the case of a detection of a chemical substance in a liquid phase, before detecting the electric state at the electrode existing in the liquid phase, a predetermined electrolytic solution is supplied around the electrode to stabilize the electric state of the electrode and then the liquid phase containing the chemical substance being measured is supplied to the electrode.