A warning device includes: a host vehicle information acquisition unit; a moving object information acquisition unit that acquires moving object information around the host vehicle; an intersection determination unit that determines whether a course of the host vehicle and a course of the moving object intersect; a distance calculation unit that calculates a distance from the host vehicle to an intersection position; an estimated crossing-time calculation unit that calculates a time that elapses before the moving object arrives at the intersection position; a threshold setting unit; and a warning unit that alerts a driver when the time is smaller than a threshold, wherein the threshold is set larger as the distance becomes larger, and is set larger when the host vehicle speed vehicle is equal to or lower than the predetermined speed than when the host vehicle speed is higher.