A fluid measurement apparatus comprising: an optical emitter capable of radiating light to an irradiation target including a fluid (A); an optical detector capable of receiving scattered light scattered by the fluid (A); and a controller that includes a generator configured to generate a frequency spectrum (S1) based on the scattered light and an estimation unit , configured to estimate a flow state of the fluid (A) based on a characteristic component of the frequency spectrum (S1), the controller being configured to estimate a flow state of a measurement target fluid (A) by causing the generator to generate a first frequency spectrum (S1) based on the measurement target fluid (A) and a second frequency spectrum (S2) based on the fluid in a known flow state, and then causing the estimation unit to compare a characteristic component of the first spectrum (S1) and a characteristic component of the second frequency spectrum (S2), characterised in that the characteristic component includes at least one of a value based on an intensity of a specific frequency in the frequency spectrum (S1, S2) and a value based on an intensity of a frequency in a specific segment, and wherein the characteristic component is a ratio of an intensity corresponding to at least one specific frequency to an intensity corresponding to at least one frequency other than the specific frequency. an optical emitter capable of radiating light to an irradiation target including a fluid (A); an optical detector capable of receiving scattered light scattered by the fluid (A); and a controller that includes a generator configured to generate a frequency spectrum (S1) based on the scattered light and an estimation unit , configured to estimate a flow state of the fluid (A) based on a characteristic component of the frequency spectrum (S1), a generator configured to generate a frequency spectrum (S1) based on the scattered light and an estimation unit , configured to estimate a flow state of the fluid (A) based on a characteristic component of the frequency spectrum (S1), the controller being configured to estimate a flow state of a measurement target fluid (A) by causing the generator to generate a first frequency spectrum (S1) based on the measurement target fluid (A) and a second frequency spectrum (S2) based on the fluid in a known flow state, and then causing the estimation unit to compare a characteristic component of the first spectrum (S1) and a characteristic component of the second frequency spectrum (S2), causing the generator to generate a first frequency spectrum (S1) based on the measurement target fluid (A) and a second frequency spectrum (S2) based on the fluid in a known flow state, and then causing the estimation unit to compare a characteristic component of the first spectrum (S1) and a characteristic component of the second frequency spectrum (S2), characterised in that the characteristic component includes at least one of a value based on an intensity of a specific frequency in the frequency spectrum (S1, S2) and a value based on an intensity of a frequency in a specific segment, and wherein the characteristic component is a ratio of an intensity corresponding to at least one specific frequency to an intensity corresponding to at least one frequency other than the specific frequency. <EOS>