A vehicular lamp comprising: a light source; a first optical element having a light-collection point on an emission side at a first position, the first optical element being configured to collect incident light from the light source at the first position; a light deflector including a mirror disposed at the first position, the mirror forward- and reverse-rotating around an axis passing through the first position, the light deflector being configured to reflect incident light from the first optical element with the mirror to deflect the light and emit the deflected light as scanning light (Ls); a second optical element configured as a convex lens, having a focal point on an incidence side at the first position and having an optical axis, the second optical element being configured to emit the scanning light (Ls) from the mirror as scanning light (Ls) that is parallel to the optical axis; a third optical element for projecting configured as a convex lens, configured to project the scanning light (Ls) from the second optical element to an irradiation region ahead, the third optical element for projecting being arranged so that an optical axis thereof is aligned with the optical axis of the second optical element; and a light shielding switching unit disposed between the second optical element and the third optical element for projecting, the light shielding switching unit having sections (Da) switched separately between a state of shielding and non-shielding of scanning light (Ls) that is incident from the second optical element; wherein the scanning light (Ls) from the mirror generates a scanning trace (Tr) by reciprocating over an incidence plane of the second optical element in the horizontal direction in a range of a scanning angle corresponding to a rotation angle of the forward and reverse rotating of the mirror around the axis, wherein the scanning trace (Tr) is the same as the irradiation region of the vehicular lamp, and wherein an incidence plane of the light shielding switching unit includes a mask control unit that is set inside of the incident plane as a rectangle that is horizontally long, the mask control unit being composed of the plurality of the sections (Da) arranged vertically and horizontally, wherein the vertical and horizontal directions of the scanning trace (Tr) are the same as the vertical and horizontal directions of the mask control unit. a light source; a first optical element having a light-collection point on an emission side at a first position, the first optical element being configured to collect incident light from the light source at the first position; a light deflector including a mirror disposed at the first position, the mirror forward- and reverse-rotating around an axis passing through the first position, the light deflector being configured to reflect incident light from the first optical element with the mirror to deflect the light and emit the deflected light as scanning light (Ls); a second optical element configured as a convex lens, having a focal point on an incidence side at the first position and having an optical axis, the second optical element being configured to emit the scanning light (Ls) from the mirror as scanning light (Ls) that is parallel to the optical axis; a third optical element for projecting configured as a convex lens, configured to project the scanning light (Ls) from the second optical element to an irradiation region ahead, the third optical element for projecting being arranged so that an optical axis thereof is aligned with the optical axis of the second optical element; and a light shielding switching unit disposed between the second optical element and the third optical element for projecting, the light shielding switching unit having sections (Da) switched separately between a state of shielding and non-shielding of scanning light (Ls) that is incident from the second optical element; wherein the scanning light (Ls) from the mirror generates a scanning trace (Tr) by reciprocating over an incidence plane of the second optical element in the horizontal direction in a range of a scanning angle corresponding to a rotation angle of the forward and reverse rotating of the mirror around the axis, wherein the scanning trace (Tr) is the same as the irradiation region of the vehicular lamp, and wherein an incidence plane of the light shielding switching unit includes a mask control unit that is set inside of the incident plane as a rectangle that is horizontally long, the mask control unit being composed of the plurality of the sections (Da) arranged vertically and horizontally, wherein the vertical and horizontal directions of the scanning trace (Tr) are the same as the vertical and horizontal directions of the mask control unit.