Japanese oak wilt has occurred in many forests in Japan since 1980. This disease is caused by pathogenic fungus, Raffaelea quercivora, vectored by the ambrosia beetle, Platypus quercivorus. Previous studies showed the beetle has positive phototaxis behavior, however its adaptive significance is still unclear. In this study, we postulated that positive phototaxis is necessary for the beetle to let them fly up to the sky immediately after their emergence from host tree, and that this taxis changes after certain flight. To confirm this hypothesis, we measured the change in phototaxis behavior of P. quercivorus before and after flight by using individuals emerged from trunk of Quercus crispula attacked in 2014. Response to the light of 60 beetles was tested ten times each before and after flying by a flight mill. The probability to show the positive phototaxis behavior increased over days of assay, and that was lower after flight than before. Time for selecting light or dark side of apparatus increased after flight. These findings suggested that the positive phototaxis of P. quercivorus and the activity of selection behavior are decreased by the course flight.