A microscope, video processing device , comprising: a microscope video acquisition unit configured to acquire a microscope video output from a surgical microscope at a predetermined frame rate; a video conversion unit configured to convert (S 10) the microscope video acquired by the microscope video acquisition unit into a three-dimensional video; a surgical instrument position determination unit configured to determine (S30), in a surgical instrument with a handle portion to which color-coded markings (4a-4f) are applied, the position of a marking for identifying the foremost end position as front end position of the surgical instrument, and configured to convert a coordinate value of the determined front end position in the microscope video into a coordinate value in the three-dimensional video to determine the front end position of the surgical instrument in the three-dimensional video converted by the video conversion unit; a distance calculation unit configured to calculate (S40) a distance between a preset patient's surgery target region and the front end position of the surgical instrument determined by the surgical instrument position determination unit; and a video output unit configured to output to a display unit an output video in which distance information indicative of the distance calculated by the distance calculation unit is displayed in the three-dimensional video, characterized in that the color-coded markings (4a-4f) are applied at an equal interval to discriminate between the front end side and back end side of the surgical instrument in the microscopic video acquired by the microscope video acquisition unit wherein the surgical instrument position determination unit is configured to determine the direction of change in the colors of the markings so as to determine the front end position of the surgical instrument. a microscope video acquisition unit configured to acquire a microscope video output from a surgical microscope at a predetermined frame rate; a video conversion unit configured to convert (S 10) the microscope video acquired by the microscope video acquisition unit into a three-dimensional video; a surgical instrument position determination unit configured to determine (S30), in a surgical instrument with a handle portion to which color-coded markings (4a-4f) are applied, the position of a marking for identifying the foremost end position as front end position of the surgical instrument, and configured to convert a coordinate value of the determined front end position in the microscope video into a coordinate value in the three-dimensional video to determine the front end position of the surgical instrument in the three-dimensional video converted by the video conversion unit; a distance calculation unit configured to calculate (S40) a distance between a preset patient's surgery target region and the front end position of the surgical instrument determined by the surgical instrument position determination unit; and a video output unit configured to output to a display unit an output video in which distance information indicative of the distance calculated by the distance calculation unit is displayed in the three-dimensional video, characterized in that the color-coded markings (4a-4f) are applied at an equal interval to discriminate between the front end side and back end side of the surgical instrument in the microscopic video acquired by the microscope video acquisition unit wherein the surgical instrument position determination unit is configured to determine the direction of change in the colors of the markings so as to determine the front end position of the surgical instrument. <EOS>