A light detection device according to an aspect of the present disclosure includes a light detector, a first layer, a first optical coupler, and a second optical coupler. The light detector includes a first photodetector and a second photodetector. The first layer is disposed above the first photodetector and the second photodetector. The first layer is light-transmissive and has a first surface and a second surface opposing the first surface. The first optical coupler is disposed on at least one surface selected from the group consisting of the first surface and the second surface. The second optical coupler is disposed on the at least one surface. The first and second optical couplers are light-transmissive and disposed above the first and second photodetectors, respectively. The second surface is closer to the light detector than the first surface.