The tomographic system of the present invention comprises a means for
taking tomographic images at plural tomographic positions in the axial
direction of the body of the subject simultaneously, a display means for
displaying the obtained plural tomographic imagers, a relative distance
between tomographic images computing unit, and a control means for
displaying and controlling the relative distance between tomographic
images and the plural tomographic images on the afore-mentioned display
means. With this, the operator can see the displayed data of the relative
distances between tomographic images and the length of the treatment
device instantaneously, and can therefore determine the insert position
of the treatment device for the subject efficiently.