A vehicular lamp comprising: a light source that radiates light; a reflector that reflects and collects the light radiated from the light source; a shade that blocks part of the light reflected and collected by the reflector; and a diffraction lens (101, 201, 301, 404) that receives incident light transmitted through the shade and radiates the incident light forward of a vehicle; wherein the diffraction lens has an incident side (102, 202, 302) and an exit side (105, 205, 305) that are both convexly shaped, includes an exit diffraction plane (107, 207, 307) that has an absolute value for the order of diffraction of 5 or greater and is disposed on the exit side, and is adapted such that the absolute value of a curvature at the surface apex of an envelope surface (108, 208, 308) of the exit diffraction plane is smaller than the absolute value of a curvature at the surface apex of an incident surface, or the absolute value of the amount of sag in the direction of the optical axis at an outer periphery of the envelope surface of the exit diffraction plane is smaller than the maximum absolute value of the amount of sag in the direction of the optical axis at an outer periphery of the incident surface; wherein the ratio of an interval between the incident surface at a radial position farthest from the optical axis (106, 206, 306) in a lens effective region and the envelope surface of the exit diffraction plane at a radial position farthest from the optical axis in a lens effective region to the interval between the surface apex of the incident surface and the surface apex of the envelope surface of the exit diffraction plane is 0.25 or higher but not higher than 0.5; wherein the order of diffraction of the exit diffraction plane is defined as (n-1)d/λ, wherein λ is a designed center wavelength, n is a refractive index of the diffraction lens, and d is a surface irregularity; and wherein the lens effective region is an actual range of light passing through the diffraction lens. a light source that radiates light; a reflector that reflects and collects the light radiated from the light source; a shade that blocks part of the light reflected and collected by the reflector; and a diffraction lens (101, 201, 301, 404) that receives incident light transmitted through the shade and radiates the incident light forward of a vehicle; wherein the diffraction lens has an incident side (102, 202, 302) and an exit side (105, 205, 305) that are both convexly shaped, includes an exit diffraction plane (107, 207, 307) that has an absolute value for the order of diffraction of 5 or greater and is disposed on the exit side, and is adapted such that the absolute value of a curvature at the surface apex of an envelope surface (108, 208, 308) of the exit diffraction plane is smaller than the absolute value of a curvature at the surface apex of an incident surface, or the absolute value of the amount of sag in the direction of the optical axis at an outer periphery of the envelope surface of the exit diffraction plane is smaller than the maximum absolute value of the amount of sag in the direction of the optical axis at an outer periphery of the incident surface; wherein the ratio of an interval between the incident surface at a radial position farthest from the optical axis (106, 206, 306) in a lens effective region and the envelope surface of the exit diffraction plane at a radial position farthest from the optical axis in a lens effective region to the interval between the surface apex of the incident surface and the surface apex of the envelope surface of the exit diffraction plane is 0.25 or higher but not higher than 0.5; wherein the order of diffraction of the exit diffraction plane is defined as (n-1)d/λ, wherein λ is a designed center wavelength, n is a refractive index of the diffraction lens, and d is a surface irregularity; and wherein the lens effective region is an actual range of light passing through the diffraction lens.