  Levels one to three of driving automation systems~(DAS) are spreading fast.
However, as the DAS functions become more and more sophisticated, not only the
driver's driving skills will reduce, but also the problem of over-trust will
become serious. If a driver has over-trust in the DAS, he/she will become not
aware of hazards in time. To prevent the driver's over-trust in the DAS, this
paper discusses the followings: 1) the definition of over-trust in the DAS, 2)
a hypothesis of occurrence condition and occurrence process of over-trust in
the DAS, and 3) a driving behavior model based on the trust in the DAS, the
risk homeostasis theory, and the over-trust prevention human-machine interface.
