Travel time is probability function which depends on congestion rate. A driver decide his/her depature time concidering not only loss by late arriving. but also uselessness by early arriving when he/she has an arrival restriction by time. It means each driver decide his/her expect sufficient time when he/she departs. We propose two hypotheses on decision of expect sufficient time and build a departure behavior model based on these hypotheses. Then this model is examined by results of a questionnaire to drivers.