A surface plasmon-field enhanced fluorescence spectroscopic measurement method comprising the steps of exciting a fluorescence substance that has labeled an analyte by surface plasmon light that has been generated by applying an excitation light to a metallic thin film and receiving the generated fluorescence by a light detection means to thereby detect the analyte, wherein: a dynamic range is expanded by adjusting a light amount of the fluorescence that is received by the light detection means comprising the step of measuring a first fluorescence signal that is output in the case in which the light detection means receives a fluorescence under a first condition in which the light amount of the fluorescence is not reduced; characterized by the steps of: providing a fluorescence amount adjusting means (32,32a,32b) for reducing a light amount of the fluorescence received by the light detection means so as to be smaller than in the first condition by a predetermined factor; measuring a second fluorescence signal that is output in the case in which the light detection means receives a fluorescence in which a light amount has been adjusted under a second condition in which the fluorescence amount adjusting means (32,32a,32b) is positioned in front of the light detection means; deciding that the first fluorescence signal is abnormal when the second fluorescence signal is not reduced by the predetermined factor and obtaining a normal fluorescence signal by multiplying the second fluorescence signal by the predetermined factor. a dynamic range is expanded by adjusting a light amount of the fluorescence that is received by the light detection means comprising the step of measuring a first fluorescence signal that is output in the case in which the light detection means receives a fluorescence under a first condition in which the light amount of the fluorescence is not reduced; characterized by the steps of: providing a fluorescence amount adjusting means (32,32a,32b) for reducing a light amount of the fluorescence received by the light detection means so as to be smaller than in the first condition by a predetermined factor; measuring a second fluorescence signal that is output in the case in which the light detection means receives a fluorescence in which a light amount has been adjusted under a second condition in which the fluorescence amount adjusting means (32,32a,32b) is positioned in front of the light detection means; deciding that the first fluorescence signal is abnormal when the second fluorescence signal is not reduced by the predetermined factor and obtaining a normal fluorescence signal by multiplying the second fluorescence signal by the predetermined factor. providing a fluorescence amount adjusting means (32,32a,32b) for reducing a light amount of the fluorescence received by the light detection means so as to be smaller than in the first condition by a predetermined factor; measuring a second fluorescence signal that is output in the case in which the light detection means receives a fluorescence in which a light amount has been adjusted under a second condition in which the fluorescence amount adjusting means (32,32a,32b) is positioned in front of the light detection means; deciding that the first fluorescence signal is abnormal when the second fluorescence signal is not reduced by the predetermined factor and obtaining a normal fluorescence signal by multiplying the second fluorescence signal by the predetermined factor.