1. A method for an obstacle alarm, the method comprising: acquiring a captured image in which an image of a visual scene of a rearward periphery of a vehicle has been captured; setting an attention-prioritized region to be the captured image; setting an outside region to be outside the attention-prioritized region in the captured image; determining whether or not an object is present in the outside region; determining a movement direction of the object; and causing a sign to be displayed at sequentially varying positions centerward from a side of the outside region where the object is present, within the attention-prioritized region displayed together with the outside region, where it is determined that the object is moving toward the center of the attention-prioritized region, the sign configured to be arrow-shaped, comprising a convex part projecting toward the center of the attention-prioritized region, wherein the sign is displayed at varying positions and enters a state of moving between two predetermined positions on the screen while flashing.