A signal acquisition device includes: a light source that oscillates pulsed laser light at a specific repetition period; an optical system that focuses the laser light onto a sample, and that collects generated fluorescence; a photodetector that detects the fluorescence collected by the optical system; an A/D converter that samples an intensity signal of the detected fluorescence, in synchronization with the repetition period of the light source unit, at a period that is an integer multiple of the repetition period, and that generates a digital intensity signal; and one or more processors comprising hardware, the one or more processors being configured to: obtain a fluorescence lifetime waveform on a basis of the generated digital intensity signal; and calculate a fluorescence lifetime coefficient from a waveform obtained by removing a region not corresponding to an exponential function from the obtained fluorescence lifetime waveform.