1. An image processing device comprising: a processing circuitry configured to: set a target place in an area of a human body structure having a tree structure in a three-dimensional image obtained by imaging the human body structure; extract the tree structure of the human body structure from the three-dimensional image; determine a path from a reference point set on a branch upstream side of the target place on the extracted tree structure to the target place; set priority for respective branches that branch off at branch points of the tree structure of the human body structure outside the path based on a positional relationship between the branches and the target place; generate, from the three-dimensional image, an initial image representing only a portion of the determined path in the entire human body structure and images for confirmation of the respective branches of the human body structure outside the path; a display device which displays an image; and a display controller which displays the generated initial image on the display device and then displays the generated images for confirmation of each step on the display device such that the respective portions of the human body structure outside the path are sequentially displayed according to the priority, wherein the processing circuitry sets the priority such that, that branches at positions closer to the target place have higher priority than branches at positions further from the target place, wherein the processing circuitry generates, from the three-dimensional image, the images for confirmation of each step in which the respective branches of the human body structure branching from the path are displayed in an order of the priority determined by the processing circuitry, and wherein the display controller displays the generated images for confirmation on the display device such that the respective branches of the human body structure branching from the path are displayed in a descending order of the determined priority.