A transmissive diffraction grating includes a polarization conversion layer, a first diffractive layer disposed on one surface side of the polarization conversion layer, and a second diffractive layer disposed on the other surface side of the polarization conversion layer. Both the first diffractive layer and the second diffractive layer include refractive index modulation structures arranged with a period P in a first direction, and diffraction efficiency for a TE polarized light component is higher than a diffraction efficiency for a TM polarized light component.