An optical beam scanner comprising: 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 (31, 32) configured to rotate around a rotational axis and reflect the light beam irradiated from the light source to scan the light beam over a range of horizontal output angles; the rotating mirror (31, 32) is rotated around the rotational axis so that the light beam is irradiated on differing positions of a mirror surface (31a, 31b) of the rotating mirror (31, 32); and the mirror surface of the rotating mirror (31, 32) has a mirror surface inclining angle θ with respect to a direction parallel to the rotational axis, the mirror surface inclining angle θ being arranged to gradually increase from a first side to a second side of the rotating mirror (31, 32) in a longitudinal direction of the mirror, parallel to a plane perpendicular to the rotational axis, so that variations in the vertical output angle of the mirror surface that occur in connection with variations in the horizontal output angle of the mirror surface are reduced; characterized in that: the mirror surface (31a, 31b) includes a first region in which the mirror surface inclining angle θ gradually increases in the direction parallel to the plane perpendicular to the rotational axis, and a second region in which: - either the mirror surface inclining angle θ is substantially the same, - or the mirror surface inclining angle θ gradually increases in the direction parallel to the plane perpendicular to the rotational axis, and the increase of the mirror surface inclining angle θ is discontinuous at the connection of the two differing regions. 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 (31, 32) configured to rotate around a rotational axis and reflect the light beam irradiated from the light source to scan the light beam over a range of horizontal output angles; the rotating mirror (31, 32) is rotated around the rotational axis so that the light beam is irradiated on differing positions of a mirror surface (31a, 31b) of the rotating mirror (31, 32); and the mirror surface of the rotating mirror (31, 32) has a mirror surface inclining angle θ with respect to a direction parallel to the rotational axis, the mirror surface inclining angle θ being arranged to gradually increase from a first side to a second side of the rotating mirror (31, 32) in a longitudinal direction of the mirror, parallel to a plane perpendicular to the rotational axis, so that variations in the vertical output angle of the mirror surface that occur in connection with variations in the horizontal output angle of the mirror surface are reduced; the mirror surface (31a, 31b) includes a first region in which the mirror surface inclining angle θ gradually increases in the direction parallel to the plane perpendicular to the rotational axis, and a second region in which: - either the mirror surface inclining angle θ is substantially the same, - or the mirror surface inclining angle θ gradually increases in the direction parallel to the plane perpendicular to the rotational axis, and - either the mirror surface inclining angle θ is substantially the same, - or the mirror surface inclining angle θ gradually increases in the direction parallel to the plane perpendicular to the rotational axis, and the increase of the mirror surface inclining angle θ is discontinuous at the connection of the two differing regions.