An information processing apparatus for medical images comprising: first acquisition means configured to acquire a plurality of positions in a three-dimensional image of a subject, obtained as positions corresponding to a sternum in the three-dimensional image of the subject; and second acquisition means configured to acquire a plurality of body surface positions of the subject, specified by an inspector as positions corresponding to the sternum of the subject, wherein the first acquisition means is configured to acquire at least a first position pM1, in the three-dimensional image of the subject, obtained as a position corresponding to the sternum at a base of the second ribs of the subject, wherein the second acquisition means is configured to acquire at least a second body surface position pU1 of the subject corresponding to the sternum at a base of the second ribs of the subject, wherein the first acquisition means is configured to further acquire at least a third position pM2, in the three-dimensional image of the subject, as a position corresponding to a lower sternum end in the three-dimensional image of the subject, wherein the second acquisition means is configured to further acquire at least a fourth body surface position pU2 of the subject at the lower sternum end of the subject, wherein the first and second acquisition means are configured to further acquire positions near the left and right second ribs pM3,pM4,pU3,pU4, and wherein the apparatus further comprises: calculation means configured to calculate a first direction as a vector defined by the first and third position and a second direction as a vector defined by the second and fourth position, and to calculate a first rigid transformation between the subject and the three-dimensional image such that the first position pM1 matches the second position pU1, and the first direction corresponding to the sternum in the three-dimensional image matches the second direction corresponding to the sternum in the subject, wherein the calculation means is further configured to execute the first rigid transformation on positions pU1 to pU4 yielding positions pU1" to pU4" respectively, and to calculate a second coordinate transformation for correcting rotation about the sternum axis, based on positions pM1 to pM4 in the three-dimensional image and positions pU1" to pU4". first acquisition means configured to acquire a plurality of positions in a three-dimensional image of a subject, obtained as positions corresponding to a sternum in the three-dimensional image of the subject; and second acquisition means configured to acquire a plurality of body surface positions of the subject, specified by an inspector as positions corresponding to the sternum of the subject, wherein the first acquisition means is configured to acquire at least a first position pM1, in the three-dimensional image of the subject, obtained as a position corresponding to the sternum at a base of the second ribs of the subject, wherein the second acquisition means is configured to acquire at least a second body surface position pU1 of the subject corresponding to the sternum at a base of the second ribs of the subject, wherein the first acquisition means is configured to further acquire at least a third position pM2, in the three-dimensional image of the subject, as a position corresponding to a lower sternum end in the three-dimensional image of the subject, wherein the second acquisition means is configured to further acquire at least a fourth body surface position pU2 of the subject at the lower sternum end of the subject, wherein the first and second acquisition means are configured to further acquire positions near the left and right second ribs pM3,pM4,pU3,pU4, and wherein the apparatus further comprises: calculation means configured to calculate a first direction as a vector defined by the first and third position and a second direction as a vector defined by the second and fourth position, and to calculate a first rigid transformation between the subject and the three-dimensional image such that the first position pM1 matches the second position pU1, and the first direction corresponding to the sternum in the three-dimensional image matches the second direction corresponding to the sternum in the subject, wherein the calculation means is further configured to execute the first rigid transformation on positions pU1 to pU4 yielding positions pU1" to pU4" respectively, and to calculate a second coordinate transformation for correcting rotation about the sternum axis, based on positions pM1 to pM4 in the three-dimensional image and positions pU1" to pU4".