A driving assist device configured to communicate with a target vehicle and each of nearby vehicles running near the target vehicle and to perform driving assist on the target vehicle, the driving assist device comprising: a reception unit (101, 102) configured to receive first vehicle information including positional information and operational information about the target vehicle, second vehicle information including positional information and operational information about each of the nearby vehicles, and a video recorded by a camera of each of the nearby vehicles; a running route computing unit configured to obtain a running route for the target vehicle on the basis of the first vehicle information; an input information determination unit configured to determine driving assist information on the basis of at least the first vehicle information, the second vehicle information, and the running route; a transmission unit configured to transmit the driving assist information determined by the input information determination unit to the target vehicle, wherein the input information determination unit selects any of the nearby vehicles that is located at a position at which a video to be used for the driving assist can be recorded, and determines the video acquired from the selected nearby vehicle as the driving assist information; an object identification unit configured to identify, on the basis of the running route and a video acquired from any of the nearby vehicles, an object existing on the running route; a collision determination unit configured to determine, on the basis of the first vehicle information, the second vehicle information, the video, and the running route, whether or not there is a possibility of a collision between the target vehicle and the object, and a type of the collision; and a warning notification unit configured to transmit a warning message to the target vehicle if the collision determination unit determines that there is a possibility of a collision with the object, wherein if the collision determination unit determines that there is a possibility of a collision with the object, the input information determination unit performs again the selection on the basis of the type of the collision. a reception unit (101, 102) configured to receive first vehicle information including positional information and operational information about the target vehicle, second vehicle information including positional information and operational information about each of the nearby vehicles, and a video recorded by a camera of each of the nearby vehicles; a running route computing unit configured to obtain a running route for the target vehicle on the basis of the first vehicle information; an input information determination unit configured to determine driving assist information on the basis of at least the first vehicle information, the second vehicle information, and the running route; a transmission unit configured to transmit the driving assist information determined by the input information determination unit to the target vehicle, wherein the input information determination unit selects any of the nearby vehicles that is located at a position at which a video to be used for the driving assist can be recorded, and determines the video acquired from the selected nearby vehicle as the driving assist information; an object identification unit configured to identify, on the basis of the running route and a video acquired from any of the nearby vehicles, an object existing on the running route; a collision determination unit configured to determine, on the basis of the first vehicle information, the second vehicle information, the video, and the running route, whether or not there is a possibility of a collision between the target vehicle and the object, and a type of the collision; and a warning notification unit configured to transmit a warning message to the target vehicle if the collision determination unit determines that there is a possibility of a collision with the object, wherein if the collision determination unit determines that there is a possibility of a collision with the object, the input information determination unit performs again the selection on the basis of the type of the collision.