A spectral module 1 comprises a substrate 2 for transmitting light L1 incident thereon from a front face 2a, a lens unit 3 for transmitting the light L1 incident on the substrate 2, a spectroscopic unit 4 for reflecting and spectrally resolving the light L1 incident on the lens unit 3, and a photodetector 5 for detecting light L2 reflected by the spectroscopic unit 4. The substrate 2 is provided with a recess 19 having a predetermined positional relationship with alignment marks 12a, 12b and the like serving as a reference unit for positioning the photodetector 5, while the lens unit 3 is mated with the recess 19. The spectral module 1 achieves passive alignment between the spectroscopic unit 4 and photodetector 5 when the lens unit 3 is simply mated with the recess 19.