PROBLEM TO BE SOLVED: To provide a hollow cross section measuring device capable of measuring a hollow cross section with ease and high accuracy. SOLUTION: A hollow cross section measuring device 3 is disposed in a tunnel, and the hollow cross section measuring device 3 is leveled by adjusting a free tripod 2 in accordance with levels 11, 12. A laser distance measuring instrument 8 is leveled by finely rotating an electromagnetic motor 6 in accordance with a level 13, and an irradiating angle of a laser beam is set at 0 deg.. While the electromagnetic motor 6 is being rotated a distance is measured by the laser distance measuring instrument 8 and is recorded. The cross-sectional shape and the cross-sectional area of the tunnel T are computed by a microcomputer 6 from the angle of the hollow cross section measuring device 3, when the range is found and distance data and the like when the range is found.