Conventional information processing apparatuses have the problem of not being able to easily extract and observe a three-dimensional region of interest from 3D voxel data. The present invention provides an information processing apparatus in which a first slice information group, which is multiple pieces of slice information obtained as a result of extraction from 3D voxel information using a first three-dimensional region mask extracting the 3D voxel information, is stored, wherein the information processing apparatus: receives input regarding a second three-dimensional region mask; acquires second mesh information constituting the second three-dimensional region mask; determines an internal region, which is a region inside the second mesh information, and an external region, which is a region outside the second mesh information, for each slice information in the first slice information group, based on the second mesh information; and outputs the first slice information group such that the internal region and the external region are visually distinguished from each other. With this information processing apparatus, it is possible to easily extract and observe a three-dimensional region of interest from 3D voxel data.