PURPOSE: To control a robot system so as to precisely and smoothly arrive at a target position even when the fluctuation of output is generated at the time of operating or decelerating the robot system.

CONSTITUTION: While receiving the transmission of moving distance data from a main central processing unit(CPU) 10, the target position to move the robot system and the 1st difference between target position data and the moving distance data are calculated at every sampling time by a CPU 11. Then, the current position data of a motor 15 are read and 2nd difference subtracting the position data of the motor before the 1st sampling time from these read data and 3rd difference subtracting the position data of the motor before the 2nd sampling time from the position data of the motor before the 1st sampling time are calculated. Then, the position data of the motor before the 1st sampling time subtracting the 3rd difference from the 2nd difference are subtracted or added so that the position of the robot system can be controlled.