ProblemTo provide a surgery assistance system that performs measurement of shapes within the abdominal cavity at high accuracy in three dimensions, and a trocar for use in such a surgery assistance system.Means for SolutionA surgery assistance system 101 includes forceps trocars 1a and 1b having retractable cameras 17a and 17b and marks 19a and 19b, a laparoscope trocar 3, forceps 4a and 4b, a laparoscope 5 having a mark 19d, an image processing device 6 that inputs the images obtained from the retractable cameras 17a and 17b and the image obtained from the laparoscope 5 and combines these images to create a three dimensional image, a three dimensional monitor 7 that outputs the three dimensional image created by the image processing device 6, and an optical tracking sensor 9. The positional relationships of the marks 19 and the corresponding cameras 17 are fixed. The positions of the marks 19 are detected by the optical tracking sensor 9, and the image processing device 6 estimates the distance between the cameras.
