A travel trajectory preparation device (2) is provided with a travel trajectory preparation unit (42) for preparing a travel trajectory that includes a linear approach section, a clothoid approach section in which a first group of clothoid curves are connected, an arc section, an escape clothoid section in which a second group of clothoid curves are connected, and a linear escape section, the travel trajectory preparation unit (42) including: an arc preparation unit (42a) for preparing an arc section that is positioned closer to the anticenter side of an arc interval than a passing target point that is separated by a predetermined distance on the anticenter side of the arc interval from the inner edge of the arc interval, the arc section having as large a radius as possible; and a clothoid preparation unit (42b) for preparing a clothoid approach section having the radius of the arc section as the radius of a final tangential arc, the starting point being in contact with the linear approach section, and the direction angle of the linear approach section being used as the direction angle of the starting point, and an escape clothoid section having the radius of the arc section as the radius of a final tangential arc, being in contact with the linear escape section, and having the direction angle of the linear escape section as the direction angle of the starting point.