A particle measuring device includes: an optical resonator that reflects laser light back and forth between two facing reflective mirrors in order to amplify an energy of that laser light and form resonant laser light; a particle transport unit that transports particles in an aerosol to be measured across a beam path of the resonant laser light; a scattered light receiving unit that receives scattered light produced when the particles in the aerosol are irradiated by the resonant laser light; and a processor that receives light reception signals from the scattered light receiving unit, wherein the processor outputs light reception pulses according to the light reception signals and calculates time intervals between the light reception pulses that are temporally adjacent.