PURPOSE: To readily design a control circuit and accurately control the attitude of a signal device by employing a numerical control unit to control a trestle.

CONSTITUTION: A trestle consists of an altitude axial drive unit for varying the altitude direction of a signal device at a command rotating speed and a bearing axis drive unit for rotating a rotatable bearer carrying the altitude axial drive unit similarly in the bearing direction. This trestle is driven by a control system consisting of a drive unit 22, a numerical controller 23, a trestle control disk 24, a main control disk 25, etc. The angular data set in the disk 25 are converted by the disk 24 into a bearing corresponding to the angle data, the number of pulses concerning the altitude direction and speed code value. The numerical controller receives these data to rotate the drive motors provided at the trestle to thereby control the attitude thereof. Thus, the numerical controller is employed to thereby readily design the control circuit and accurately control the attitude of the signal device.