An on-vehicle device mounted on a vehicle includes an imaging unit that captures an image of a wide angle range through a curved light receiver, a moving-object detector that detects a moving object approaching an own vehicle from a mounting direction of the imaging unit and from any direction other than the mounting direction, based on the image captured by the imaging unit, a collision-risk determination unit that determines a degree of collision risk indicating a possibility of collision between the moving object detected by the moving-object detector and the own vehicle, and a moving-object warning unit that warns presence of the moving object included in an image portion in which a distortion of the image is a predetermined value or more, and warns the presence of the moving object according to the degree of collision risk determined by the collision-risk determination unit.