A configuration includes: a target-motion prediction unit (5) that calculates predicted movement ranges of one or more other vehicles (60) based on target tracking; an inter-target collision possibility estimator (6) that estimates a collision possibility based on overlap of predicted movement ranges of the other vehicles (60); a target-motion re-prediction unit (7) that again calculates predicted movement ranges to avoid collision when the collision possibility between the other vehicles (60) exists; an own-motion prediction unit (10) that calculates a predicted movement range of a user's vehicle (50) based on an observation result; and an own-collision possibility estimator (11) that estimates collision possibilities between the user's vehicle (50) and the other vehicles (60) based on overlap of the final predicted movement ranges of the other vehicles (60) and the predicted movement range of the user's vehicle (50).