1. A method of registering medical images, the method comprising: determining whether a probe is disposed on a reference point of a target, the reference point being a physiological feature in the target that is not modified over time; calculating, when the probe is disposed on the reference point, a transformation relation between a first medical image and a second medical image of a different modality than that of the first medical image, by calculating the transformation relation between coordinates of the reference point based on a coordinate system of the first medical image and coordinates of the reference point based on a coordinate system of the second medical image, wherein the first medical image is obtained by using the probe; supplementing the transformation relation by aligning a first object included in the first medical image and a second object included in the second medical image; and obtaining, from the second medical image, a sectional image corresponding to a sectional image of the first medical image, by using the transformation relation which has been supplemented, wherein, in response to the first object and the second object being different, the transformation relation is supplemented by matching a geometric disposition structure between the first object and the second object with a pre-stored geometric disposition structure, wherein the obtaining comprises: obtaining coordinates of the sectional image of the first medical image, transforming the coordinates of the sectional image of the first medical image into coordinates of the second medical image by using a function of the transformation relation, and obtaining, from the second medical image, the sectional image having the transformed coordinates.