A fine particle detection device according to the present disclosure includes: a first irradiation portion configured to radiate excitation light to a flow passage in which a fine particle flows to excite fluorescent light from the fine particle; a first separation portion configured to separate the excitation light and the fluorescent light from light that has been radiated to the flow passage by the first irradiation portion; a first detection portion configured to detect the fluorescent light separated by the first separation portion; a second irradiation portion configured to radiate the excitation light separated by the first separation portion to the flow passage to excite the fluorescent light from the fine particle; a second separation portion configured to separate the excitation light and the fluorescent light from light that has been radiated to the flow passage by the second irradiation portion; and a second detection portion configured to detect the fluorescent light separated by the second separation portion.