PURPOSE: To provide plural sensors around a cutting torch without increasing the number of slip rings which transmit a signal to keep the height of the cutting torch in about a fixed level from a material to be cut.

CONSTITUTION: A vertically movable block 4b is freely vertically movably provided on a carriage 3 and a rotatable block 7 is freely rotatably provided on the vertically movable block 4b. While an electric relay part 8 having slip rings 8a is provided at the lower end of the vertically movable block 4b, laser sensors 9a-9d are fitted to arms 7a and 7b provided on the rotatable block 7, a comparing device 11 is provided on the arm 7b. A signal from each laser sensor is compared by the comparing device 11 and only the optimum signal is outputted as a controlling signal. Thus, regardless to the number of the laser sensors, the height of the cutting torch is controlled through one slip ring.