This paper examines the preliminary-announcement and display function of the robot's following action and intention, especially about the direction of motion and the speed of motion for mobile robot which moves on a 2D plane. Based on the result of the fundamental examination, the validity of the preliminary-announcement and display at around 1 second before the actual motion has been verified on a 2D plane. Moreover we have found that human being tends to understand the change of speed of the mobile robot more with some transforming object than with some changing-color object. Comparing two types of the proposed methods, the efficiency of the preliminary-announcement and display by indicating the continuous information as drawing with beam-light more than by displaying a state as lighting lamp or using blowouts have been declared. Moreover, we have found that the scheduled path needs some amount of length for a person to understand the mobile robot's following action.