1. A method of registering medical images, the method comprising: calculating, when a probe is disposed on a reference point of a target, a transformation relation for registering a first medical image and a second medical image having a different modality from the first medical image by using the reference point, wherein the first medical image is obtained by using the probe; and obtaining a sectional image of the second medical image corresponding to a sectional image of the first medical image, from the second medical image, by using the transformation relation.