A method for detecting a non-luminescent target particle dispersed and randomly moving in a sample solution using an optical system of a confocal microscope or multi-photon microscope, comprising: (a) a step for preparing a sample solution containing target particles, and labeling particles of which the average outer diameter is less than 15% of the diameter of a photodetection region of the optical system, binding two or more molecules of the labeling particles per molecule of the target particles in the sample solution, and forming a non-luminescent complex of which the outer diameter is 15% or more of the diameter of the photodetection region; and, (b) a step for calculating the number of molecules of the complex in the sample solution prepared in the step (a), comprising: a step for moving the location of the photodetection region of the optical system in the sample solution, a step for generating chronological light intensity data by detecting light containing substantially constant background light from the photodetection region while moving the location of the photodetection region of the optical system in the sample solution, a step for individually detecting a decrease in light intensity in the chronological light intensity data that occurs when the complex has entered the photodetection region as a signal representing the presence of an individual complex, and a step for counting the number of the complexes detected during movement of the location of the photodetection region by counting the number of signals representing the presence of the individually detected complexes. (a) a step for preparing a sample solution containing target particles, and labeling particles of which the average outer diameter is less than 15% of the diameter of a photodetection region of the optical system, binding two or more molecules of the labeling particles per molecule of the target particles in the sample solution, and forming a non-luminescent complex of which the outer diameter is 15% or more of the diameter of the photodetection region; and, (b) a step for calculating the number of molecules of the complex in the sample solution prepared in the step (a), comprising: a step for moving the location of the photodetection region of the optical system in the sample solution, a step for generating chronological light intensity data by detecting light containing substantially constant background light from the photodetection region while moving the location of the photodetection region of the optical system in the sample solution, a step for individually detecting a decrease in light intensity in the chronological light intensity data that occurs when the complex has entered the photodetection region as a signal representing the presence of an individual complex, and a step for counting the number of the complexes detected during movement of the location of the photodetection region by counting the number of signals representing the presence of the individually detected complexes. a step for moving the location of the photodetection region of the optical system in the sample solution, a step for generating chronological light intensity data by detecting light containing substantially constant background light from the photodetection region while moving the location of the photodetection region of the optical system in the sample solution, a step for individually detecting a decrease in light intensity in the chronological light intensity data that occurs when the complex has entered the photodetection region as a signal representing the presence of an individual complex, and a step for counting the number of the complexes detected during movement of the location of the photodetection region by counting the number of signals representing the presence of the individually detected complexes.