Disclosed is a resonant wavelength measurement apparatus, including a light source and a measurement unit. The measurement unit has a guided-mode resonance filter and a photosensitive element. The guided-mode resonance filter has a plurality of resonant areas, and each resonant area has a different filtering characteristic, to receive first light in the light source transmitted by a sensor or receive second light in the light source reflected by the sensor. The first light has a first corresponding pixel on the photosensitive element, the second light has a second corresponding pixel on the photosensitive element, and the first corresponding pixel and the second corresponding pixel correspond to a same resonant wavelength.