Provided is a particle counter including: a light source; a light superimposition unit configured to superimpose light beams; an irradiation optical system configured to irradiate a fluid in a flow passage with one of a plurality of light beams from the light source; a detection optical system configured to make a part of scattered light beams by a particle in the fluid enter the light superimposition unit; a reference optical system configured to split another one of the plurality of light beams into a plurality of reference light beams and makes the reference light beams enter the light superimposition unit; and a counting unit configured to count the particles on the basis of detection signals corresponding to an interference light beam received by a light receiver. The interference light beam is generated by interference between the scattered light beam and one of the reference light beams at the light superimposition unit, and is received by the light receiver corresponding to the reference light beam.