A calibration method for calibrating a body fluid component measuring instrument configured to measure a component in a body fluid based on a detection value related to reflected light obtained by projecting light on a test strip containing a chromogenic reagent that reacts with the component in the body fluid, the calibration method comprising: an acquisition step of measuring and acquiring a spectral reflection characteristic (Ri) of each of a plurality of samples prepared by using the test strip by attaching the body fluid having the component to each of the test strips; a reference estimation step of estimating, by integrating the spectral characteristics for each wavelength (λ), a reference detection value (Yi), that is, a detection value on each of the samples when a reference light source is used, based on a spectral radiation characteristic (Es) of the reference light source that is a reference for a light source to be mounted on the body fluid component measuring instrument, and based on each of the spectral reflection characteristics (Ri) obtained; an individual estimation step of estimating, by integrating the spectral characteristics for each wavelength (λ), an individual detection value (Xi), that is, a detection value on each of the samples when an individual light source is used, based on a spectral radiation characteristic (Er) of the individual light source that is the same type as the reference light source and that is to be mounted on a calibration target instrument, namely, the body fluid component measuring instrument, and based on each of the spectral reflection characteristics (Ri) obtained; and a determination step of determining a calibration curve by which the detection value obtained on the test strip on the calibration target instrument having the individual light source mounted thereon is converted into the detection value when the reference light source is used, by fitting each combination of the reference detection value (Yi) and the individual detection value (Xi) estimated for each of the samples to a predetermined function. an acquisition step of measuring and acquiring a spectral reflection characteristic (Ri) of each of a plurality of samples prepared by using the test strip by attaching the body fluid having the component to each of the test strips; a reference estimation step of estimating, by integrating the spectral characteristics for each wavelength (λ), a reference detection value (Yi), that is, a detection value on each of the samples when a reference light source is used, based on a spectral radiation characteristic (Es) of the reference light source that is a reference for a light source to be mounted on the body fluid component measuring instrument, and based on each of the spectral reflection characteristics (Ri) obtained; an individual estimation step of estimating, by integrating the spectral characteristics for each wavelength (λ), an individual detection value (Xi), that is, a detection value on each of the samples when an individual light source is used, based on a spectral radiation characteristic (Er) of the individual light source that is the same type as the reference light source and that is to be mounted on a calibration target instrument, namely, the body fluid component measuring instrument, and based on each of the spectral reflection characteristics (Ri) obtained; and a determination step of determining a calibration curve by which the detection value obtained on the test strip on the calibration target instrument having the individual light source mounted thereon is converted into the detection value when the reference light source is used, by fitting each combination of the reference detection value (Yi) and the individual detection value (Xi) estimated for each of the samples to a predetermined function.