1. A volume image generating method comprising: transmitting an ultrasonic signal to a target body divided into a plurality of regions and generating a first sub-volume image corresponding to a first region from among the plurality of regions of the target body, based on a response signal reflected from the target body; generating a second sub-volume image corresponding to a second region contacting the first region from among the plurality of regions; connecting the second sub-volume image to the first sub-volume image according to a location relationship between the first region and the second region of the target body; and re-generating the second sub-volume image based on a concordance rate between sectional images of the first and second sub-volume images that contact each other, and connecting the re-generated second sub-volume image to the first sub-volume image.