An animal blood cell measuring apparatus comprising: a specimen preparation section for preparing a measurement specimen from blood of an animal; a characteristic information obtaining section for obtaining characteristic information indicating a characteristic of the measurement specimen, from the measurement specimen prepared by the specimen preparation section, the characteristic information comprising fluorescence intensity information and scattered light intensity information; and a controller configured for performing operations comprising: (a) classifying aggregate reticulocytes contained in the blood from other blood cells, based on the characteristic information obtained by the characteristic information obtaining section, wherein the operation (a) comprises: demarcating a red-blood-cell type coordinate area that includes red blood cells and reticulocytes, on a scattergram having a coordinate axis representing the fluorescence intensity and a coordinate axis representing the scattered light intensity; obtaining a distribution of blood cell count with respect to the fluorescence intensity, based on the plot data present within the red-blood-cell type coordinate area; obtaining fluorescence intensity X that corresponds to a peak of the blood cell count and a variance σ of the distribution from the distribution; performing calculation of Thr = X + α · σ based on the obtained fluorescence intensity X, the obtained variance σ, and a coefficient α that is applied to measurement of the aggregate reticulocytes of the animal, thereby calculating a threshold value Thr of the fluorescence intensity, and demarcating an aggregate-type coordinate area that includes the aggregate reticulocytes by using the threshold value Thr; and (b) outputting information regarding a number of the classified aggregate reticulocytes based on a number of plot data contained in the aggregate-type coordinate area. a specimen preparation section for preparing a measurement specimen from blood of an animal; a characteristic information obtaining section for obtaining characteristic information indicating a characteristic of the measurement specimen, from the measurement specimen prepared by the specimen preparation section, the characteristic information comprising fluorescence intensity information and scattered light intensity information; and a controller configured for performing operations comprising: (a) classifying aggregate reticulocytes contained in the blood from other blood cells, based on the characteristic information obtained by the characteristic information obtaining section, (a) classifying aggregate reticulocytes contained in the blood from other blood cells, based on the characteristic information obtained by the characteristic information obtaining section, wherein the operation (a) comprises: demarcating a red-blood-cell type coordinate area that includes red blood cells and reticulocytes, on a scattergram having a coordinate axis representing the fluorescence intensity and a coordinate axis representing the scattered light intensity; obtaining a distribution of blood cell count with respect to the fluorescence intensity, based on the plot data present within the red-blood-cell type coordinate area; obtaining fluorescence intensity X that corresponds to a peak of the blood cell count and a variance σ of the distribution from the distribution; performing calculation of Thr = X + α · σ based on the obtained fluorescence intensity X, the obtained variance σ, and a coefficient α that is applied to measurement of the aggregate reticulocytes of the animal, thereby calculating a threshold value Thr of the fluorescence intensity, and demarcating an aggregate-type coordinate area that includes the aggregate reticulocytes by using the threshold value Thr; and (b) outputting information regarding a number of the classified aggregate reticulocytes based on a number of plot data contained in the aggregate-type coordinate area. demarcating a red-blood-cell type coordinate area that includes red blood cells and reticulocytes, on a scattergram having a coordinate axis representing the fluorescence intensity and a coordinate axis representing the scattered light intensity; obtaining a distribution of blood cell count with respect to the fluorescence intensity, based on the plot data present within the red-blood-cell type coordinate area; obtaining fluorescence intensity X that corresponds to a peak of the blood cell count and a variance σ of the distribution from the distribution; performing calculation of Thr = X + α · σ based on the obtained fluorescence intensity X, the obtained variance σ, and a coefficient α that is applied to measurement of the aggregate reticulocytes of the animal, thereby calculating a threshold value Thr of the fluorescence intensity, and demarcating an aggregate-type coordinate area that includes the aggregate reticulocytes by using the threshold value Thr; and (b) outputting information regarding a number of the classified aggregate reticulocytes based on a number of plot data contained in the aggregate-type coordinate area. (b) outputting information regarding a number of the classified aggregate reticulocytes based on a number of plot data contained in the aggregate-type coordinate area.