Provided is an image processing device capable of effectively displaying the details of a plurality of different branches included in a structure that is divided into a plurality of branches. An image processing device 100 reads the entire image of a coronary artery region, extracts a coronary artery region A from the read image data, displays the coronary artery region A, calculates cores 41, 42, and 43 of three coronary arteries A1, A2, and A3, and calculates the lengths of blood vessels. In addition, when an operator uses a GUI 33 that is displayed in parallel to the entire image of the coronary artery region A to designate an arbitrary scale position on the GUI 33, a CPU 101 calculates positions on the blood vessels A1, A2, and A3 corresponding to the designated scale position. The CPU 101 displays vertical tomographic images 321, 322, and 323 at the calculated corresponding positions in a detailed image display region 32.