The present invention provides a particle diameter distribution measuring method, a particle diameter distribution measuring device, and a measuring program which decreases the dependence of the calculation of particle diameter distribution on sample concentration, and can measure with higher precision by setting a concentration correction unique to a specific measuring sample in a particle diameter distribution measuring device. The measuring sample is measured by changing its concentration. Concentration correction constants for correcting detection values of detectors according to the concentration of the sample are found. The detection values of the respective detectors are corrected by using the concentration correction constants, and the particle diameter distribution is measured by using the corrected detection values of the respective detectors.
