A light emission device of one embodiment reduces zero-order light included in output of an S-iPM laser. The light emission device includes a light emission unit and a phase modulation layer. The phase modulation layer has a base layer and modified refractive index regions each including modified refractive index elements. In each unit constituent region centered on a lattice point of an imaginary square lattice set on the phase modulation layer, the distance from the corresponding lattice point to each of the centers of gravity of the modified refractive index elements is greater than 0.30 times and is not greater than 0.50 times of the lattice spacing. In addition, the distance from the corresponding lattice point to the center of gravity of the modified refractive index elements as a whole is greater than 0 and is not greater than 0.30 times of the lattice spacing.