PURPOSE: To improve work efficiency by calculating a relative position between a robot and a work and a deviation between the relative position and a moving target position from a distance between a robot and the work, a diagonal angle, and a moving amount provided for a robot and displaying a calculating result.

CONSTITUTION: A moving target position predetermined by a work test is stored in a memory 15 through a man machine interface 14 of an input part 10 in a manner to be classified by each work. A boom 2 is moved by means of a boom moving device 19, measurement reference points A and B of an electric pole 6 are caused to enter the view of field of monitoring cameras 5 and 5', and measuring reference points A and B are indicated by a measuring point indicator l7. A distance gauge board 18 inputs position information at an indication point to a calculator 12. The calculator 12 determines a distance between a work and a robot and a diagonal angle to determine an initial value. The calculator 12 calculates the present position of a robot from a movement amount of the boom 2 and the initial value, inputted from the calculator 12 and the boom moving device 19, and analogue-displays a deviation between the present position and the moving target position of a memory 15 on a display part 13.