A robot controlling method which guarantees an accurate motion along the path by eliminating the influence of the motion in the preceding path section on a part toward the end of one path section. In a motion instruction, a path guarantee section of a path from '2' to '3' is designated in advance by specifying the length, time, or path guarantee ratio. A path plan EFGH of the motion in the path from '1' to '2' is so made that the motion section expressed by DHGK (D is the end point of the motion in the path from '1' to '2') is the path guarantee section designated in the motion instruction. Therefore, the motion in the path from '1' to '2' does not affect the motions after the point of time expressed by point D or K, and hence the motion along the path '2' to '3' in the path guarantee section is guaranteed.