An automatic analysis method for analyzing a blood sample containing bacteria and impurities, the method comprising: introducing a substance that destroys the impurities into the sample; separating by a centrifugal separator the impurities and the bacteria from each other in the sample into which the substance has been introduced; taking out the bacteria from the sample using a filter that takes out the bacteria from the sample from which the impurities and the bacteria have been separated; reading correspondence data describing correspondence between a numerical value representing an amount of the impurities remaining on the filter and a concentration of the bacteria in the sample from a storage unit that stores the correspondence data; and estimating a concentration of the bacteria in the sample by referring to the correspondence data using a numerical value representing the amount of the impurities remaining on the filter after taking out the bacteria from the sample, wherein the sample contains blood cells as the impurities, the substance is a surfactant, the surfactant comprises at least one of: an anionic surfactant having a hydrophilic moiety and a hydrophobic moiety, the hydrophobic moiety being a chain hydrocarbon; or a surfactant having a hydrophilic moiety and a hydrophobic moiety, the hydrophobic moiety having a cyclic hydrocarbon, the filter is a filtration filter that separates the impurities and the bacteria by filtering the sample, and the estimating the concentration of the bacteria includes detecting the amount of impurities remaining on the filter using an image obtained by imaging without staining the impurities remaining on the filter, and referring to the correspondence data using the amount of the impurities detected using the image. introducing a substance that destroys the impurities into the sample; separating by a centrifugal separator the impurities and the bacteria from each other in the sample into which the substance has been introduced; taking out the bacteria from the sample using a filter that takes out the bacteria from the sample from which the impurities and the bacteria have been separated; reading correspondence data describing correspondence between a numerical value representing an amount of the impurities remaining on the filter and a concentration of the bacteria in the sample from a storage unit that stores the correspondence data; and estimating a concentration of the bacteria in the sample by referring to the correspondence data using a numerical value representing the amount of the impurities remaining on the filter after taking out the bacteria from the sample, wherein the sample contains blood cells as the impurities, the substance is a surfactant, the surfactant comprises at least one of: an anionic surfactant having a hydrophilic moiety and a hydrophobic moiety, the hydrophobic moiety being a chain hydrocarbon; or a surfactant having a hydrophilic moiety and a hydrophobic moiety, the hydrophobic moiety having a cyclic hydrocarbon, an anionic surfactant having a hydrophilic moiety and a hydrophobic moiety, the hydrophobic moiety being a chain hydrocarbon; or a surfactant having a hydrophilic moiety and a hydrophobic moiety, the hydrophobic moiety having a cyclic hydrocarbon, the filter is a filtration filter that separates the impurities and the bacteria by filtering the sample, and the estimating the concentration of the bacteria includes detecting the amount of impurities remaining on the filter using an image obtained by imaging without staining the impurities remaining on the filter, and referring to the correspondence data using the amount of the impurities detected using the image. detecting the amount of impurities remaining on the filter using an image obtained by imaging without staining the impurities remaining on the filter, and referring to the correspondence data using the amount of the impurities detected using the image.