Apparatus wherein an identical field of view of an object to-be-observed is imaged in two directions different from each other and wherein the image in one of the directions and the image in the other direction are reproduced and displayed as a left eye image and a right eye image respectively, thereby to perform the stereoscopic version of the object to-be-observed, comprising means to indicate one mark on each of the left eye image and the right eye image, and means to move both the marks to any desired positions on the respective images. The mark moving means has the function of interlockingly moving both the marks by equal distances in the same direction on the respective images, and the function of singly moving only the mark on one of the images as the position of the mark on the other image is kept fixed, and it is provided with means to control the change-over between the interlockingly moving state and the singly moving state. In moving the marks to points on the respective images as correspond to desired points on the object to-be-observed, both the marks may be interlockingly moved until the mark on the other image arrives at the desired point, and subsequently, with the mark position on the other image kept fixed, only the mark on the one image may be singly moved to the desired point.