An actual-size observation mode in which an observer performs observation by being immersed in a virtual three-dimensional space in an actual size and a reduced-size observation mode in which the observer performs observation by reducing a virtual three-dimensional space computer graphics image are provided. A virtual reality presentation device includes an observation mode setting unit for setting, as an observation mode, the actual-size observation mode or the reduced-size observation mode; a position and orientation information acquisition unit for acquiring position and orientation information of the observer; and a generation unit for generating a computer graphics image from computer graphics data representing the virtual three-dimensional space in accordance with the set observation mode and the position and orientation information.