A measuring apparatus and a measuring method are configured to measure a concentration of an organic solvent in a sample solution, measure a concentration of the organic solvent in a concentration control solution, calculate a mixture amount by which the concentration control solution is mixed into the sample solution of a preset amount so that the concentration of the organic solvent in the sample solution is equal to a preset concentration based on the two concentrations, mix the concentration control solution of the calculated mixture amount with the sample solution of the preset amount, supply a mixture solution obtained by the mixing unit to a measurement region in which a bioactive substance is immobilized in advance, and measure an interaction between the bioactive substance and the sample substance in the mixture solution based on a result of measuring a refraction index of a light incident on the measurement region.