1. A medical image processing apparatus comprising: a virtual endoscopic image generation unit configured to generate a virtual endoscopic image of a tubular structure represented in a three-dimensional medical image, and which is viewed from the inside of the tubular structure; an observation path setting unit configured to set an observation path along the tubular structure in the three-dimensional medical image; an observation direction setting unit configured to set an observation direction of the tubular structure along the observation path; a viewpoint setting unit configured to set a viewpoint on the observation path; and a visual range determination unit configured to identify, based on the three-dimensional medical image, the position of a wall region of the tubular structure present in a local observation direction at the viewpoint and in the vicinity of the local observation direction, and to estimate, based on a positional relationship between the viewpoint and the wall region, a global observation direction at the viewpoint, and to determine a visual range of the virtual endoscopic image in such a manner that image information about a region located in the global observation direction with respect to the viewpoint is represented at a central part of the virtual endoscopic image, wherein the virtual endoscopic image generation unit is configured to generate, from the three-dimensional medical image, the virtual endoscopic image representing a view within the visual range at the viewpoint.