PURPOSE: To maintain the reference attitude of a robot at all times without being influenced by the installation angle of a robot base when the robot is installed by regulating to constant values the position and angle of a laser beam emission part, slit, light receiving element, mirror, etc.

CONSTITUTION: A vertical arm 5 is positioned with an angle to the horizontal direction and forms an angle θ with respect to a horizontal arm 6, and the center line of the vertical arm 5 and the reference line of a robot base 2 pinch an angle (r) in between. In this condition, a laser beam 25 emitted from a laser beam emission part 14 passes through a slit 15 while part of the beam passes through a half mirror 16 and is received by a light receiving element 17. The remainder is reflected by the half mirror 16, passed through a slit 18, and received by another light receiving element 20. These light receiving elements 17 and 20 send light reception signals to a CPU 23, which on the basis of the given signals, sends to a control board 24 a signal to instruct the motion of a robot 1 so that the robot 1 returns to the original attitude. As a result, the reference attitudes of all robots belonging to one model can be maintained constant at all times.