A bio-molecule detecting device that enables a high-sensitivity measurement is provided. The orientation direction of third complexes included in blood plasma is switched by switching the vibration direction of an orientation control light. The orientation direction of the third complexes is switched between two directions in which the intensities of an electric field, which is generated between two gold nanoparticles included in the third complexes by surface plasmon resonance, are significantly different. Therefore, the intensity of fluorescence generated from the third complexes is significantly changed by the change in the orientation direction of the third complexes.
