Acquired is the internal information of a scattering medium more accurately and easily, with the influence of an instrumental function taken into account, even where noise is contained in a measurement waveform.In a method for measuring a scattering medium, pulse light with a predetermined wavelength is made incident on a scattering medium which is a measurement object and a scattering medium for reference (S01b, S02b), the pulse light transmitted inside each of the scattering media is detected to acquire a light detection signal (S01c, S02c), the measurement waveform is acquired on the basis of the detected light detection signal (S01d, S02d), a parameter of a function showing the theoretical waveform of the measurement object is specified in such a manner that the result of convolution operation on the theoretical waveform of the measurement object and the measurement waveform of the reference is made equal to the result of convolution operation on the theoretical waveform of the reference and the measurement waveform of the measurement object (S03), and calculation is made for the internal information of the scattering medium on the basis of the theoretical waveform shown by the function (S04).