1. A measuring method for performing monitoring measurement on two or more objects to be measured by a measuring instrument, which comprises a telescope unit for sighting an object to be measured, a distance measuring unit for projecting a distance measuring light through said telescope unit and for measuring a distance to said object to be measured, an image pickup unit for taking an image in sighting direction and for acquiring a digital image, an angle detecting unit for detecting a directional angle in the sighting direction of said telescope unit, and an automatic sighting unit for making said telescope unit automatic sighting to said object to be measured, comprising a step of rotating said telescope unit in horizontal direction and in vertical direction and of scanning a predetermined range being set up so as to include two or more objects to be measured, a step of acquiring digital images at a predetermined time interval so that there are two or more images which include the same object to be measured while scanning, a step of detecting an image of the object to be measured in said digital image and of setting up a minimal rectangle surrounding the image of the object to be measured, a step of overlapping said minimal rectangles obtained in two or more digital images and of carrying out integrated processing to obtain positions of said objects to be measured in the image, a coarse measurement step of calculating a composite directional angle of each of the objects to be measured respectively based on a position in the image obtained by integrated processing and on a directional angle of a sighting axis, and a step of associating said composite directional angle obtained by said coarse measurement with each of the objects to be measured and of storing said composite directional angle as target values for automatic sighting.