A volumetric data connecting apparatus, includes a reference point determining device for having an operator determine reference points A, B and C which are not on the same straight line on first volumetric data V; a connection point a determining device for having the operator determine a connection point a corresponding to said reference point A on second volumetric data v; an auxiliary line q displaying device for displaying “a section fb of the second volumetric data v” selected by the operator and a curve q which results from the crossing of said section fb and “a spherical surface Q having the distance between the reference points AB as its radius and the connection point a as its center”.