1. An apparatus for measuring the depth of a three-dimensional (3D) image, the apparatus comprising: a display panel unit which produces a 3D image by displaying a left-eye image and a right-eye image; a depth measurement unit which measures projecting distances or recessed distances of the 3D image and a real object; a parallax measurement unit which measures a distance between pupils of an experimenter based on the projecting distances or recessed distances of the 3D image and the real objects; and a depth value calculation unit which calculates an average value of the projecting distances or recessed distances of the real object with respect to a plurality of experimenters, which are measured when a change in distance between pupils is the same as a change in distance between pupils measured by adjusting the projecting distance or recessed distance of the 3D image, and determines the calculated average value as a depth value of the 3D image.