A biological information detection device includes a light source, an image capturing device, and one or more arithmetic circuits. The light source projects dots formed by light onto a target including a living body. The image capturing device includes photodetector cells and generates an image signal representing an image of the target onto which the dots are projected. The one or more arithmetic circuits detect a portion corresponding to at least a part of the living body in the image by using the image signal and calculate biological information of the living body by using image signal of the portion.