1. Apparatus for discriminating the type and counting the number of white blood corpuscles comprising means for irradiating with light a predetermined area of a slide supporting stained white blood corpuscles, means for producing a microscopic image of said white blood corpuscles which is analyzed into a plurality of given wavelength components over the entire range of visible light, means for producing an electric signal corresponding to the density of light transmitted through each sampling point of the resulting microscopic image of each of said plurality of wavelength components, a memory device for storing said electric signal, means for normalizing said electric signal, means for comparing the normalized electric signal and a reference data signal established for each type of said white blood corpuscles and producing a similarity signal indicating the similarity, means for detecting and storing a first similarity signal corresponding to the maximum similarity and a second similarity signal corresponding to the next maximum similarity thus determined and for detecting and storing the type of the white blood corpuscles corresponding to said maximum value and the type of the white blood corpuscles corresponding to said value next to the maximum, means responsive to the result of said detections for counting the number of the white blood corpuscles at respective sampling points, and means for estimating the number of the white blood corpuscles of respective types in a predetermined area of said slide.