1. A three-dimensional display apparatus, comprising: a plurality of imaging units for obtaining a plurality of images having a parallax with respect to a subject viewed from different viewpoints by imaging the subject from different viewpoints; a three-dimensional processing unit for performing three-dimensional processing for three-dimensional display on the plurality of images and performing the three-dimensional processing on an object to be displayed in the three-dimensionally displayed three-dimensional image in a superimposed manner; a display unit for performing at least the three-dimensional display of the three-dimensional image; a distance information calculation unit for calculating distance information of the three-dimensional image; an imaging control unit for controlling the imaging units to image the subject at a predetermined time interval; an evaluation value calculation unit for calculating an evaluation value which includes an evaluation value of at least one of a luminance and a high frequency component of the images obtained by the imaging units at the predetermined time interval; and a control unit for controlling the distance information calculation unit and the three-dimensional processing unit to respectively perform the calculation of distance information and the three-dimensional processing on the plurality of images and the object when the evaluation value has changed by an amount exceeding a predetermined threshold value, wherein the three-dimensional processing unit is a unit that changes a relative position of the object with respect to the three-dimensional image in a three-dimensional space based on the distance information such that overlapping of the object and the three-dimensional image on top of each other is prevented when the three-dimensional display is performed.