To reduce variations in locus distortion accuracy in individual postures due to a minute deviation of gear engagement and that of a shaft in an arm casing in a robot when an original point position is registered.

A reference original point position is registered in the robot (a step 1). A correction original point position near the reference original point position where a locus distortion amount of the arm becomes small is specified while executing arm expansion/contraction operations for each station (steps 2, 3, and 4). An original point position correction amount in each posture is calculated by comparing the correction original point position with the reference original point position (a step 5). The arm is operated while switching to the corresponding correction original point position or after superimposing a correction amount onto a command value during arm operation to each station.