1. An evaluation method of a spheroid for evaluating a collapse degree of the spheroid from an image obtained by imaging the spheroid, the evaluation method comprising: specifying a spheroid region taken up by the spheroid out of the image including the spheroid and a surrounding region thereof; obtaining an average value of an optical density of the spheroid and a magnitude of a variation of the optical density in the spheroid from an image density of the spheroid region; obtaining a circularity of the spheroid from a contour of the spheroid region; obtaining a sharpness of the spheroid from the image densities of the spheroid and the surrounding region thereof; and obtaining the collapse degree of the spheroid by substituting the average value of the optical density, the magnitude of the variation of the optical density, the circularity and the sharpness into a predetermined operational expression.