A floating particle detection device (1, 2, 3) comprising: a laser light irradiator that includes a laser light emitting element including a front-side edge surface configured to emit an irradiation laser beam with which a detection-target region where floating particles are present is irradiated and a back-side edge surface configured to emit a back-monitor-use laser beam which travels in a direction opposite to a travel direction of the irradiation laser beam, and a back-monitor-use light receiving element disposed in a position where the back-monitor-use laser beam is incident, the back-monitor-use light receiving element configured to generate a first detection signal according to an amount of incident light; a scattered light receiver configured to selectively receive light of a predetermined polarization component among scattered light (Ls) of the irradiation laser beam, the scattered light (Ls) being generated when a floating particle is irradiated, thereby generating a second detection signal; and an identification processor configured to identify a type of the floating particle on a basis of the first detection signal and the second detection signal; wherein the incident light entering the back-monitor-use light receiving element includes the back-monitor-use laser beam and backscattered light (Lbs) travelling toward the laser light irradiator among the scattered light (Ls) of the irradiation laser beam with which the floating particle is irradiated, wherein the identification processor includes a first identification unit and a direct-current/alternating-current separator configured to separate the first detection signal generated by the back-monitor-use light receiving element into a first direct-current component which corresponds to the back-monitor-use laser beam and an alternating-current component which corresponds to the backscattered light (Lbs) travelling toward the laser light irradiator; wherein the first identification unit is configured to identify the size of the floating particle on a basis of a degree of a change of the alternating-current component. a laser light irradiator that includes a laser light emitting element including a front-side edge surface configured to emit an irradiation laser beam with which a detection-target region where floating particles are present is irradiated and a back-side edge surface configured to emit a back-monitor-use laser beam which travels in a direction opposite to a travel direction of the irradiation laser beam, and a back-monitor-use light receiving element disposed in a position where the back-monitor-use laser beam is incident, the back-monitor-use light receiving element configured to generate a first detection signal according to an amount of incident light; a scattered light receiver configured to selectively receive light of a predetermined polarization component among scattered light (Ls) of the irradiation laser beam, the scattered light (Ls) being generated when a floating particle is irradiated, thereby generating a second detection signal; and an identification processor configured to identify a type of the floating particle on a basis of the first detection signal and the second detection signal; wherein the incident light entering the back-monitor-use light receiving element includes the back-monitor-use laser beam and backscattered light (Lbs) travelling toward the laser light irradiator among the scattered light (Ls) of the irradiation laser beam with which the floating particle is irradiated,