1. A detection device for a vehicle, for detecting an obstacle within a target region by emitting a laser beam to the target region, comprising: a) a beam source for emitting a laser beam in pulse shape; b) an actuator for changing an irradiation direction of the laser beam; c) a target region setting circuit for setting the target region within which the laser beam is scanned; d) a scan trajectory setting circuit for setting a scan trajectory; e) an irradiation pattern setting circuit for setting an irradiation pattern of irradiation positions irradiated by the laser beam, wherein the target region, the scan trajectory, and the irradiation pattern are determined based upon at least one of the following factors: a speed of the vehicle, a direction of the vehicle, and a steering of the vehicle, the irradiation pattern determines the irradiation positions of the laser beam in pulse shape on the scan trajectory; and frequency of the irradiation positions in the target region is weighted partially high in a portion of the target region where an object is detected.