A surface plasmon-field enhanced fluorescence measurement device comprising: a sensor structure that is configured from a sensor member that is provided with a dielectric member, a metallic thin film formed on the dielectric member, and a ligand immobilized region formed on the metallic thin film, and a well member affixed onto the sensor member, wherein said well member has a through hole at the position of the ligand immobilized region, and said through hole is configured for storing a solution that includes an analyte; and a device body that is provided with at least a light source for applying excitation light to the metallic thin film of the sensor structure, such that the excitation light is incident into the dielectric member and reflected on the metallic thin film on the side of the dielectric member of the sensor structure, and a light detection means for detecting fluorescence when a fluorescent substance held in the ligand immobilized region has been excited, wherein the sensor structure is configured so as to be used attachably to and detachably from the device body or so as to be used while being affixed to the device body, characterized by a stirring device a position adjusting means configured to move the sensor structure and the light source in a relative manner for an adjustment, wherein, for setting the application position of the excitation light, the position adjusting means is adapted to align the optical axis of the excitation light to a position B in which an amount of an analyte captured by the ligand in the ligand immobilized region is highest, wherein the position B is a predetermined distance away from the position of the centre of gravity of a bottom surface region that is defined by the through hole, the position B being obtained by following steps: stirring a sample solution in the through hole, dyeing the ligand immobilized region, for example by using a gold colloid, after stirring, researching a distribution of the amount of the analyte captured by the ligand and then obtaining the position B having the highest amount of the analyte. a sensor structure that is configured from a sensor member that is provided with a dielectric member, a metallic thin film formed on the dielectric member, and a ligand immobilized region formed on the metallic thin film, and a well member affixed onto the sensor member, wherein said well member has a through hole at the position of the ligand immobilized region, and said through hole is configured for storing a solution that includes an analyte; and a device body that is provided with at least a light source for applying excitation light to the metallic thin film of the sensor structure, such that the excitation light is incident into the dielectric member and reflected on the metallic thin film on the side of the dielectric member of the sensor structure, and a light detection means for detecting fluorescence when a fluorescent substance held in the ligand immobilized region has been excited, wherein the sensor structure is configured so as to be used attachably to and detachably from the device body or so as to be used while being affixed to the device body, characterized by a stirring device a position adjusting means configured to move the sensor structure and the light source in a relative manner for an adjustment, wherein, for setting the application position of the excitation light, the position adjusting means is adapted to align the optical axis of the excitation light to a position B in which an amount of an analyte captured by the ligand in the ligand immobilized region is highest, wherein the position B is a predetermined distance away from the position of the centre of gravity of a bottom surface region that is defined by the through hole, the position B being obtained by following steps: stirring a sample solution in the through hole, dyeing the ligand immobilized region, for example by using a gold colloid, after stirring, researching a distribution of the amount of the analyte captured by the ligand and then obtaining the position B having the highest amount of the analyte. stirring a sample solution in the through hole, dyeing the ligand immobilized region, for example by using a gold colloid, after stirring, researching a distribution of the amount of the analyte captured by the ligand and then obtaining the position B having the highest amount of the analyte.