A three-dimensional image display method, includes: displaying a three-dimensional image including a left eye image signal and a right eye image signal displayed at a display focus angle; determining whether to change a viewing focus angle with respect to the display focus angle; calculating a pixel distance between the left eye image signal and the right eye image signal if it is determined to change the viewing focus angle; and displaying indicator marks at positions spaced as much as a half of the pixel distance from a center of a screen in leftward and rightward directions.