Abandoned or illegally parked bicycles are very serious problems in many places. One of the important countermeasures to deal with this problem is to cultivate consciousness not to park illegally. In this study, we conducted a questionnaire survey to high school students who frequently use bicycle, and tried to find factors that make them refrain from illegal parking. Two factors are found to be relevant, namely, a good manner and a law-abiding mind. Especially, in order to increase law-abiding mind, it is important to have an experience of enforced rules such as wearing bicycle helmet or restricting the range of commuting by bicycle, as well as the traffic safety education in elementary and secondary schools. Those who have these experiences in their childhood are less likely to commit illegal parking when they grow up.