Abstract: A rotation displaying device for displaying the rotating speed of an engine, especially, that of an agricultural machine such as a combine harvester, in colors classified by the low speed, standard speed and high speed. The device comprises a rotary shaft rotating at a speed proportional to the rotating speed of the engine, and a color pattern plate urged in one direction by the centrifugal force produced by the rotation of the rotary shaft. The color pattern plate is provided on its surface with a pattern of three different colors, and the color pattern changing with the successive displacement of the color pattern plate is viewed through a single central displaying opening of a display plate to display the low speed, standard speed and high speed of the engine.