A structure applies a pre-load to a rolling bearing, which makes pre-load control easier than heretofore and enables low cost production. A pre-load applying structure is configured to apply a pre-load to a bearing of a scanning part of a three-dimensional survey device. The three-dimensional survey device includes the bearing having an inner ring to which a vertically rotating shaft is fixed, a scanning mirror attached to the vertically rotating shaft, and a motor for rotationally driving the vertically driving shaft. The pre-load applying structure has a sleeve that engages with an outer ring of the bearing, a plate spring that detachably engages with the sleeve and is fastened to a housing body with a screw, and a ring that detachably join the sleeve and the plate spring. The plate spring applies the pre-load to the outer ring via the sleeve by elastic deforming.