An object owner determining unit generates object owner information by determining an owner of an identified object identified by an object identification unit, out of the occupants identified by an occupant identification unit, using occupant identification information and object identification information. When getting out of an occupant is detected by the occupant identification unit, an object misplacement determining unit determines whether or not an object owned by the occupant who gets out is misplaced in the vehicle using the object owner information about the occupant who gets out. When the object misplacement determining unit determines that an object owned by the occupant who gets out is misplaced in the vehicle, the warning unit provides a warning.