An image taken by a real camera is repeatedly obtained, and position and orientation information determined in accordance with a position and an orientation of a real camera in a real space is repeatedly calculated. A virtual object or a letter to be additionally displayed on the taken image is set as an additional display object, and based on a result of recognition of a sound inputted into a sound input device, at least one selected from the group consisting of a display position, an orientation, and a display form of the additional display object is set. A combined image repeatedly generated by superimposing on the taken image the set additional display object with reference to a position in the taken image in accordance with the position and orientation information is displayed on a display device.