To provide a concentration calculating module configured to measure the concentrations of two constituents simultaneously with higher accuracy.
The concentration measuring module includes a light source configured to emit light into a housing; a first light receiving unit configured to have sensitivity to a wavelength of output light of the light source and receive light radiated from inside the housing; and a second light receiving unit configured to have sensitivity to a longer wavelength than the first light receiving unit and receive light radiated from inside the housing. The light source, the first light receiving unit, and the second light receiving unit are arranged to have a positional relationship in which a light emitting surface of the light source faces a light receiving surface of the first light receiving unit, and a normal to a light receiving surface of the second light receiving unit is orthogonal to, of a line through the light source and the first light receiving unit, a line segment corresponding to the inside of the housing, and a length X of, of the line through the light source and the first light receiving unit, the line segment corresponding to the inside of the housing and then a length Y of, of a line including the normal to the light receiving surface of the second light receiving unit, a line segment corresponding to the inside of the housing satisfy Y/X>1. The concentration measuring module calculates the concentrations of two constituents simultaneously on the basis of first and second signals output from the first and second light receiving units.