A concentration measurement device 100 includes a light source 22 for generating incident light to a measurement space 10A, a photodetector 24 for receiving light emitted from the measurement space, and an arithmetic control circuit 26 for calculating a concentration of a measurement fluid on the basis of an output of the photodetector, and the light source includes a first light-emitting element 22a for generating light having a first wavelength, and a second light-emitting element 22b for generating light having a second wavelength, and the concentration measurement device is configured so as to calculate the concentration using either light of the first wavelength or the second wavelength on the basis of the pressure or temperature of the measurement fluid.