1. An image measurement apparatus, comprising: a tissue region recognition unit configured to recognize a tissue region from an image which is imaged by staining tissue including a measurement object and a non-measurement object; a partial image extraction unit configured to extract images of a predetermined size and a fixed magnification from the tissue region; a mask generation unit configured to generate a mask to remove a non-measurement object region, which is a region in which the non-measurement object exists, from the tissue region for each of the extracted images; a whole mask generation unit configured to generate a provisional whole mask by merging masks generated for each of the images and generate a whole mask by merging portions which are not masked in the provisional whole mask, the portions adjacent to each other into one or more object regions; a measurement unit configured to measure, for each of the images extracted by the partial image extraction unit, information on the measurement object contained in the images; and a region information computation unit configured to compute, based on the measured information and the whole mask, information on the measurement object for each of the object regions, wherein the measurement unit measures the cell nuclei count according to staining intensity for each of the images extracted by the partial image extraction unit, and the region information computation unit computes, based on the measured cell nuclei count according to staining intensity and the whole mask, a positive ratio for each of the object regions.