An image measurement apparatus, comprising: a lighting unit configured to emit a first narrowband light that is a light with a bandwidth (i) narrower than a bandwidth of a visible light and (ii) including a dominant wavelength of a color of a positive cell nucleus; an image obtaining unit configured to obtain an examination image by capturing an image of a pathologic examination specimen to which the first narrowband light is emitted; a cell nuclei extracting unit configured to extract pixels of positive cell nuclei from the examination image by comparing pixel values of the examination image with a predetermined threshold; a positive proportion calculating unit configured to calculate a proportion of the positive cell nuclei among cell nuclei included in the pathologic examination specimen, using the pixels of the positive cell nuclei extracted by the cell nuclei extracting unit; and an output unit configured to output the proportion calculated by the positive proportion calculating unit, characterized in that the lighting unit is further configured to emit a broadband light that is a light with a bandwidth broader than the bandwidth of the first narrowband light, the image obtaining unit is further configured to obtain a reference image by capturing an image of a pathologic examination specimen to which the broadband light is emitted, and in that the image measurement apparatus further comprises: a dominant wavelength calculating unit configured to calculate a dominant wavelength of a color of a positive cell nucleus included in the reference image and to set the wavelength of a narrowband light emitted by the lighting unit to the dominant wavelength determined from the reference image; and a threshold calculating unit configured to calculate, as the predetermined threshold, a threshold for extracting pixels of positive cell nuclei from the reference image by performing threshold processing, based on a light intensity of the dominant wavelength calculated by the dominant wavelength calculating unit. a lighting unit configured to emit a first narrowband light that is a light with a bandwidth (i) narrower than a bandwidth of a visible light and (ii) including a dominant wavelength of a color of a positive cell nucleus; an image obtaining unit configured to obtain an examination image by capturing an image of a pathologic examination specimen to which the first narrowband light is emitted; a cell nuclei extracting unit configured to extract pixels of positive cell nuclei from the examination image by comparing pixel values of the examination image with a predetermined threshold; a positive proportion calculating unit configured to calculate a proportion of the positive cell nuclei among cell nuclei included in the pathologic examination specimen, using the pixels of the positive cell nuclei extracted by the cell nuclei extracting unit; and an output unit configured to output the proportion calculated by the positive proportion calculating unit, characterized in that the lighting unit is further configured to emit a broadband light that is a light with a bandwidth broader than the bandwidth of the first narrowband light, the image obtaining unit is further configured to obtain a reference image by capturing an image of a pathologic examination specimen to which the broadband light is emitted, and in that the image measurement apparatus further comprises: a dominant wavelength calculating unit configured to calculate a dominant wavelength of a color of a positive cell nucleus included in the reference image and to set the wavelength of a narrowband light emitted by the lighting unit to the dominant wavelength determined from the reference image; and a threshold calculating unit configured to calculate, as the predetermined threshold, a threshold for extracting pixels of positive cell nuclei from the reference image by performing threshold processing, based on a light intensity of the dominant wavelength calculated by the dominant wavelength calculating unit. a dominant wavelength calculating unit configured to calculate a dominant wavelength of a color of a positive cell nucleus included in the reference image and to set the wavelength of a narrowband light emitted by the lighting unit to the dominant wavelength determined from the reference image; and a threshold calculating unit configured to calculate, as the predetermined threshold, a threshold for extracting pixels of positive cell nuclei from the reference image by performing threshold processing, based on a light intensity of the dominant wavelength calculated by the dominant wavelength calculating unit.