The results showed that the turning angles are basically at random, and there is no correlation among these conditions and turning angles. Fig.3 shows the relation-ship between initial swimming angle and reacted turning angle. Rotating reaction was indicated by plotted on 360 deg area in Fig.3. Therefore, we have to forgive to predict which reaction may occur. 3.2 Reaction Behaviors to The Scanning Laser beam Next, the reaction properties of Euglena to the scanning laser beam were exam-ined. The scanning frequency was varied during 1 - 20 Hz. Basic reactions on these experiments were, above mentioned avoiding reaction, rotating reaction, no reaction and swimming along the laser line with spiral rotation. The last reaction was considered that the rotating reaction was observed from the different (upward in Fig.2 (b)) angle. The investigation results showed no correlation. Therefore, it is very difficult to predict which reaction will be appeared or to predict the turning angle. The amount of not reacted examples has a correlation to the scanning frequency and the length of the scanning line. This is corresponded to the probability ratio that the laser beam is not irradiated to the sensory spot of the Euglena when the Euglena swims across the scanning laser line. Above observation experiments showed that the response of Euglena is basically random, and it is very difficult to control the swimming direction to our aiming di-rection by irradiating the laser beam. The only possibility is to change the swim-ming direction from the present swimming direction. Therefore, the control effi-ciency is worse than the control method using galvano-taxis when we control an individual cell. 4 Mechanism of The Gathering and The Group Formation The reaction of Positive phototaxis has not seen in the individual cell level obser-vations. However, when a laser was irradiated into the high population density culture media, a gathering and group formation of Euglena was seen in the media. Fig.4 shows an example. In this experiment, fixed spot laser beam was irradiated to the high density (2600 cell/mm^) culture medium. This photograph was taken after 10 minutes irradiation. Therefore, it is necessary for the motion control of Euglena group to investigate how the Euglena gather and form the group. Therefore, the influence of cell population density of culture media and the power of the laser beam on the gathering and group formation process was measured when a laser spot light is irradiated. Fig.5 summarizes the changes of the density distribution around the laser spot light through the time passage. First, a ring-shaped group was formed around the spot laser beam, and then, the high density area enlarged and beam area was finally covered with Euglena