A solid-state imaging device (10, 10A, 10B) comprising: a pixel part (20, 20A, 20B) having unit pixel groups (200, 200A, 200B) arranged therein, the unit pixel groups (200, 200A, 200B) including pixels (PXL11, PXL12, PXL21, PXL22) for visible light that perform photoelectric conversion that generates pixel signals; and a reading part for reading the pixel signals from the pixel part, wherein the pixels (PXL11, PXL12, PXL21, PXL22) for visible light have a light-receiving sensitivity to infrared light, and in an infrared reading mode, the reading part is configured to add together the pixel signals due to infrared light read from the pixels (PXL11, PXL12, PXL21, PXL22) for visible light, each of the unit pixel groups (200, 200A, 200B) include a plurality of photoelectric conversion parts (PD11, PD12, PD21, PD22) configured to photoelectrically convert light incident from one surface side and corresponding to the plurality of visible light wavelength bands, each of the plurality of photoelectric conversion parts (PD 11, PD12, PD21, PD22) includes a red photoelectric conversion part corresponding to a red region, a green photoelectric conversion part (PD11, PD22) corresponding to a green region, and a blue photoelectric conversion part corresponding to a blue region, in a first mode, the reading part is configured to output, in each one of the plurality of unit pixel groups (200, 200A, 200B), signals read from the red photoelectric conversion part, the green photoelectric conversion part (PD11, PD22), and the blue photoelectric conversion part, characterized in that in a second mode comprising the infrared reading mode, the reading part is further configured to add together, in each one of the plurality of unit pixel groups (200, 200A, 200B), the pixel signals read from the red photoelectric conversion part, the green photoelectric conversion part (PD11, PD22), and the blue photoelectric conversion part. a pixel part (20, 20A, 20B) having unit pixel groups (200, 200A, 200B) arranged therein, the unit pixel groups (200, 200A, 200B) including pixels (PXL11, PXL12, PXL21, PXL22) for visible light that perform photoelectric conversion that generates pixel signals; and a reading part for reading the pixel signals from the pixel part, wherein the pixels (PXL11, PXL12, PXL21, PXL22) for visible light have a light-receiving sensitivity to infrared light, and in an infrared reading mode, the reading part is configured to add together the pixel signals due to infrared light read from the pixels (PXL11, PXL12, PXL21, PXL22) for visible light, each of the unit pixel groups (200, 200A, 200B) include a plurality of photoelectric conversion parts (PD11, PD12, PD21, PD22) configured to photoelectrically convert light incident from one surface side and corresponding to the plurality of visible light wavelength bands, each of the plurality of photoelectric conversion parts (PD 11, PD12, PD21, PD22) includes a red photoelectric conversion part corresponding to a red region, a green photoelectric conversion part (PD11, PD22) corresponding to a green region, and a blue photoelectric conversion part corresponding to a blue region, in a first mode, the reading part is configured to output, in each one of the plurality of unit pixel groups (200, 200A, 200B), signals read from the red photoelectric conversion part, the green photoelectric conversion part (PD11, PD22), and the blue photoelectric conversion part, characterized in that in a second mode comprising the infrared reading mode, the reading part is further configured to add together, in each one of the plurality of unit pixel groups (200, 200A, 200B), the pixel signals read from the red photoelectric conversion part, the green photoelectric conversion part (PD11, PD22), and the blue photoelectric conversion part.