This paper presents electro-hydraulic servo systems of a robotic excavator with a contour control algorithm. It is very important to precisely move the bucket tip of the excavator to a desired trajectory. There have been many studies to accurately control the bucket dealing with the non-linearity in the hydraulic boom, arm, and bucket cylinders. Beginning with these conventional methods, a new method that focuses on keeping contours rather than just following position commands is presented. In the leveling work, for example, it is more important to maintain linear contour than chasing a position goal. The contour control shares the control effort to make the bucket stay on the path, while slightly sacrificing the position tracking accuracy. After the kinematics of the excavator system were analyzed, the contour control algorithm was developed. The algorithm was applied to leveling work with a real excavator. The experiments showed better performance than using position control alone.