The invention relates to an object detector. The object detector includes a light source; an optical system that converts a light beam emitted from the light source into a predetermined state; a deflector that deflects and scans the light beam passing through the optical system, and that irradiates the light beam onto an object; and a photo detector that detects reflected light or scattered light. A first size of a light emitting region of the light source is different from a second size of the light emitting region, wherein the first size is a first width of the light emitting region in a first direction, and the second size is a second width of the light emitting region in a second direction. One of the first direction and the second direction corresponding to a smaller one of the first size and the second size coincides with a direction in which angular resolution is higher.