There is provided an image processing apparatus and its method allowing a user to specify a desired 3D area without cutting volume data. The present invention provides an image processing apparatus specifying a desired 3D area on volume data, which includes a display section that displays the volume data, an input section that a user inputs a 2D path for the volume data displayed on the display section, a path rendering section that converts the 2D path into a 3D path according to analysis of relation between the 2D path and volume data, and a 3D area specification section that specifies the desired 3D area based on the 3D path.