PURPOSE: To have deceleration control in response to the counter of each rapidly changing point by comparing a plurality of threshold values with the change amount per unit time of a displacement signal and by controlling the feed speed of tracer head relative to the model in accordance with the zone in which the change amount is function of threshold value.

CONSTITUTION: When the processing comes to a point, at the time T1, where the model contour is changing rapidly, the output signal ' from a calculator circuit 24 increases rapidly, and output signals aWc from comparators 25W27 vary from '0' to '1' sequentially, so that the output signal d from an OR gate OR1 which takes logical sum of output signals of rise sensing circuits 28W30, becomes '1' at the rise of signals aWc. Change of the output signal d from said OR gate OR1 increases gradually the individual values CA, CB of counters 34, 35, that will increase the attenuation ratio of an attenuator 38 to cause stepped decrease of its output signal Va, and accordingly the output signal Vb from an accelerator/decelerator circuit 39 will also decrease gradually from the velocity command signal Vcmd with a time constant τ1. The level of the tangential velocity Vr given by a velocity calculator circuit lowers proportional to level drop of the signal Vb from said accelerator/decelerator circuit 39, and thereby the feeding speed is reduced.