PURPOSE: To control a speed change of a motor to an S shape in an arbitrary range by so arbitrarily setting an acceleration and a time at polygonal lines that an acceleration during a period reaching a designated speed from a present speed becomes an S-shaped speed change approximated by a polygonal line.

CONSTITUTION: A present speed set by a speed setter 1 is started to be changed with a speed change starting speed as S0, an acceleration value Ac1 of a head number stored in a ROM 4 is read and speed-changed by a CPU 3. A changed speed ΔV1 of this zone is stored in a predetermined area of a RAM 5, and a real speed of a motor 8 is monitored with S1=(S0+ΔV1) as next changing acceleration point. When the motor 8 is accelerated and the fact that an output of a speed detector 9 reaches a speed S1 is detected by a speed deviation detector 6, an acceleration Ac2 of next number is read from the ROM 4, and the acceleration is altered. Thus, the acceleration is so sequentially controlled as to become an S-shaped speed change approximated by a polygonal line, and the speed of the motor 8 is controlled.