To provide a device for measuring fine particles without any measurement error due to undershooting, and a method for analyzing the fine particles for sensitively measuring those with a small particle diameter.

A fine particle constituent analysis device for measuring the size of a fine particle according to a signal being screened by a wavelength- screening means is provided with a low-pass filter as the wavelength-screening means and a DC component operation means 61 for inputting output from a signal amplification means and outputting a DC component signal, where the DC component operation means 61 is composed of a differential operation means 65 for inputting output from the low-pass filter 60 and that from the DC component operation means 61 and subtracting a DC component from the output of the low-pass filter 60 and a particle diameter operation means for calculating the size of the fine particle based on an output signal from the differential operation means 65. Also, for a signal with a peak within a specific range out of screened signals, a measurement signal or noise is judged based on at least either the time integration of waveform or the half-value width of a peak value and statistical data being obtained in advance.