A vehicle behavior detection device mounted on an own vehicle detects own vehicle's behavior, in particular driver's right or left turn behavior at an intersection on a roadway. The vehicle behavior detection device is a microcomputer system having a CPU capable of providing an intended direction acquiring section, a turn direction acquiring section, a coincidence judgment section and an information output section. The intended direction acquiring section obtains an intended direction toward which the own vehicle is turning. The turn direction acquiring section acquires a direction to which the own vehicle turns. The coincidence judgment section detects whether or not the intended direction coincides with the turn direction of the own vehicle. The information output section provides warning regarding wide right or left turn of the own vehicle when the judgment result indicates that the intended direction does not coincide with the turn direction of the own vehicle.