The concentration measurement device 100 includes an electric unit 20 having a light source 22 and a photodetector 24, a fluid unit 10 having a measurement cell 1, optical fibers 11 and 12 for connecting the electric unit 20 and the fluid unit 10 and is configured to measure the concentration of the fluid in the measurement cell by detecting the light incident from the light source 22 to the measurement cell and then emitted from the measurement cell by the photodetector 24, where optical connection parts 32 and 34 connected to the optical fibers 11, 12 and the light source 22 or the photodetector 24 are integrally provided in the electric unit 20.