A lamp to be mounted on a vehicle, the lamp comprising: a light source; a lens unit including a projection lens which is disposed such that at least a portion of light emitted from the light source passes therethrough, and a holder which supports the projection lens; and an adjustment mechanism configured to adjust a reference position of an optical axis of the projection lens, wherein the adjustment mechanism includes: a reference axis perpendicular to the optical axis and which intersects with a focal point of the projection lens; a first screw configured to adjust the reference position in a first direction; a second screw configured to adjust the reference position in a second direction intersecting with the first direction; a first transmission mechanism configured to rotate the lens unit about the reference axis in accordance with rotation of the first screw; characterised: in that the lamp comprises a second transmission mechanism configured to move at least a portion of the lens unit along the reference axis in accordance with rotation of the second screw, and in that an acting point (93c1) of the second transmission mechanism applying a force onto the lens unit to move the optical axis is disposed in a plane formed by the optical axis and the reference axis. a light source; a lens unit including a projection lens which is disposed such that at least a portion of light emitted from the light source passes therethrough, and a holder which supports the projection lens; and an adjustment mechanism configured to adjust a reference position of an optical axis of the projection lens, wherein the adjustment mechanism includes: a reference axis perpendicular to the optical axis and which intersects with a focal point of the projection lens; a first screw configured to adjust the reference position in a first direction; a second screw configured to adjust the reference position in a second direction intersecting with the first direction; a first transmission mechanism configured to rotate the lens unit about the reference axis in accordance with rotation of the first screw; characterised: in that the lamp comprises a second transmission mechanism configured to move at least a portion of the lens unit along the reference axis in accordance with rotation of the second screw, and in that an acting point (93c1) of the second transmission mechanism applying a force onto the lens unit to move the optical axis is disposed in a plane formed by the optical axis and the reference axis. a reference axis perpendicular to the optical axis and which intersects with a focal point of the projection lens; a first screw configured to adjust the reference position in a first direction; a second screw configured to adjust the reference position in a second direction intersecting with the first direction; a first transmission mechanism configured to rotate the lens unit about the reference axis in accordance with rotation of the first screw; characterised: in that the lamp comprises a second transmission mechanism configured to move at least a portion of the lens unit along the reference axis in accordance with rotation of the second screw, and in that an acting point (93c1) of the second transmission mechanism applying a force onto the lens unit to move the optical axis is disposed in a plane formed by the optical axis and the reference axis. in that the lamp comprises a second transmission mechanism configured to move at least a portion of the lens unit along the reference axis in accordance with rotation of the second screw, and in that an acting point (93c1) of the second transmission mechanism applying a force onto the lens unit to move the optical axis is disposed in a plane formed by the optical axis and the reference axis.