Provided is a particle detector capable of increasing detection sensitivity of fluorescence emitted from biologically derived particles. This particle detector for detecting biologically derived particles (101) has a main surface (11), and is provided with a substrate (10) which collects biologically derived particles (101) on the main surface (11), a light-emitting element (21) which irradiates the particles (100) collected on the main surface (11) with an excitation light (EL), and a light-receiving element (34) which receives the fluorescence (F) emitted from the particles (100) when these are irradiated with the excitation light (EL) from the light-emitting element (21). The optical axis of a Fresnel lens (32) and the beam direction (OD1) of the excitation light (EL) intersect. The main surface (11) is a mirror surface.
