A light detection device includes a light detector including first detectors and second detectors both disposed along a main surface; a light coupling layer disposed on or above the light detector; and a light shielding film disposed on the light coupling layer. The light coupling layer includes a first low-refractive-index layer, a first high-refractive-index layer that is disposed on the first low-refractive-index layer and includes a first grating, and a second low-refractive-index layer that is disposed on the first high-refractive-index layer. The light shielding film includes a light transmitting region and a light shielding region adjacent to the light transmitting region. The light transmitting region faces two or more first detectors included in the first detectors, and the light shielding region faces two or more second detectors included in the second detectors.