PURPOSE: To provide a servo motor speed controller which can secure a high feed accuracy with a simple constitution.

CONSTITUTION: A rotary encoder 11 detects the rotating speed of a reference rotary shaft 1a of a printing machine 1 and produces a pulse signal of the frequency proportional to the detected rotating speed. The rotating speed ratio, i.e., a speed ratio of a feed roll 3 is set at a register 16 against the rotating speed of the shaft 1a. An MPU 12 calculates a thinning rate based on the speed ratio set at the register 16 and outputs a thinning rate command to a rate multi-counter 17. The multi-counter 17 thins the pulse signals generated from a pulse generator 11 in the thinning ratio set according to the command signal given from the MPU 12 and outputs the thinned pulse signals to a driver 15. The driver 15 defines the thinned pulse signals as the command value and drives servo motor 7 based on this command value and the rotating speed signal received form a rotary encoder 14.