1. A three-dimensional shape measuring apparatus which measures a three-dimensional shape of an object, said three-dimensional shape measuring apparatus comprising: a mirror which reflects light from the object; an image capturing unit configured to capture a captured image including both a real image and a virtual image of the object, the virtual image being formed using said mirror; a light amount changing unit configured to change a light amount of one of the real image and the virtual image; an image separating unit configured to specify, as the one of the real image and the virtual image, a portion included in a first captured image and a second captured image and having a light amount different between the first captured image and the second captured image, the first captured image being influenced by the change caused by said light amount changing unit and the second captured image being uninfluenced, and to specify, as the other of the real image and the virtual image, a portion included in the first captured image and the second captured image and having a same light amount; and a reconstruction unit configured to reconstruct the three-dimensional shape of the object, using the real image and the virtual image that are specified by said image separating unit.