PURPOSE:To shorten the time required for processing by calculating intermediate angle position data where the moving speed is within an allowable range and outputting this data at intervals of a certain time to move a robot to a target interpolation point and calculating angle position data of the next interpolation point thereafter. CONSTITUTION:A variation operating means C calculates the variation of angle position data, which is outputted from an interpolating means A at intervals of a certain time, as the moving speed of each shaft, and a discriminating means D discriminates whether this operated variation exceeds an allowable value or not. If it is discriminated that the variation exceeds the allowable value, a intermediate angle position operating means E is operated. This means E calculates plural intermediate angle position data so that the variation of angle position data given to a servo motor driving circuit B does not exceed the allowable value. After outputting plural operated intermediate angle position data at intervals of a certain time, a control means F operates the means A to calculate coordinate values of the next interpolation point.