An optical beam scanner includes a light source, an optical scanner configured to scan a light beam irradiated from the light source, and an input optical system configured to direct the light beam irradiated from the light source to the optical scanner, wherein the optical scanner includes a rotating mirror configured to rotate around a rotational axis and reflect the light beam irradiated from the light source; the rotating mirror is rotated around the rotational axis so that the light beam is irradiated on differing positions of a mirror surface of the rotating mirror; and the mirror surface of the rotating mirror has a mirror surface inclining angle with respect to a direction parallel to the rotational axis that is arranged to gradually increase from a first side to a second side of the rotating mirror in a direction parallel to a plane perpendicular to the rotational axis.