PURPOSE: To drive a body to be checked along a planned line by arranging a screen and an iTV over the body to be checked, picking up the spot image of a laser beam projected on the screen, and obtaining the average position of the spot images at a plurality of positions.

CONSTITUTION: A movable light receiving device 2 is provided in a shield digging machine B in a tunnel. The reference laser beam 1a from a laser oscillator 1 which is provided in a tunnel coating segment A is projected on the screen 3 of the movable light receiving device 2, and its spot image is picked up by the iTV4. The output of the iTV4 is sent to an image processing unit 5 (microcomputer), and the average coordinates of the spot images on the screen 3 at a plurality of moving positions of the digging machine B are computed. The digging machine B is driven so that the deviation between the reference beam 1a and the direction of the movement becomes the minimum. In this constitution, digging machine B which is the body to be checked is driven along the planned line.