PURPOSE: To obtain the title device automatically controlling operation speed of reaping part comprising a reaping speed detecting means, a traveling speed detecting means, a reaping speed setting means and a controlling means by making a discovered reaping speed coincident with a target value corresponding to a discovered traveling speed.

CONSTITUTION: In a control device of an operating speed of a reaping part of a combine, a reaping part A is connected to an output side of a ring cone speed regulator 18. When movement of a handling lever 57 of a hydraulic speed change gear 9 to shift speed of a crawler 11 is detected by a lever sensor, a target value corresponding to a target value of a shifter 38 of the ring cone speed regulator 18 is set based on the detected value by the lever sensor. When difference between the detected value of shifter sensor to discover the position of the shifter 38 and the target value, the shifter 38 is driven by a ring cone motor 42 so that both the values are coincident. Under a condition of the completion of the control, a target reaping speed of the reaping part A is set from the detected value of a traveling speed sensor to discover a traveling speed of a traveling part G and the shifter 38 is driven and controlled in such a way that the detected value of the reaping speed sensor is coincident with the target reaping speed.