[Object] To provide a chemical sensor provided with a spectral filter excellent in spectral characteristic, a chemical sensor module, a chemical substance detection apparatus, and a chemical substance detection method.[Solving Means] A chemical sensor according to the present technology is provided with a substrate and a plasmon absorption layer. On the substrate, the photodetection unit is formed. The plasmon absorption layer is laminated on the substrate and has a metal nanostructure that generates plasmon absorbency.