PURPOSE: To improve reliability of turning speed control by calculating the turning speed on the basis of the pulse cycle time of pulse to be input from a pulse generating means, and calculating the turning speed through a process of selecting the last pulse cycle when it is judged that the pulse cycle is affected by a backlash.

CONSTITUTION: A pulse generating means 10 is provided for generating a pulse signal in a cycle corresponding to the rotation angle of an output part 20a of a driving means 20 for turning a turning table 4 through meshing of a driving gear 7 with a driven gear 6. The pulse cycle Tn is calculated by a cycle calculating means 13 on the basis of the pulse signal and the time signal from a timer means 11, and the change states of this pulse cycle and the last pulse cycle are judged by a judging means 14. The last pulse cycle is selected when this pulse cycle is changed by the specified value or more in relation to the last pulse cycle, this pulse cycle is selected 16 when this pulse cycle time is changed by the specified value or less, and the present turning speed is output 17 on the basis of the selected pulse cycle.