A biological analysis device includes a CPU as a control device which determines a boundary between a first bandwidth in which a temporal change in a signal intensity is large and a second bandwidth which is located closer to a high frequency side than the first bandwidth and in which a temporal change in the signal intensity is less than the first bandwidth in a plurality of intensity spectra related to frequencies calculated sequentially with regard to light reflected and received inside a biological body through radiation of a laser beam, and calculates a biological index related to a blood flow of the biological body from a signal intensity within a frequency range in which the boundary is an upper limit in the intensity spectrum.