A particle counting system includes a collector, a liquid input/output operation executing means, and a particle counter. The collector performs a collecting operation to introduce the surrounding air into a container storing a liquid to collect airborne particles in the liquid. The liquid input/output operation executing means executes a series of liquid input/output operations to supply an additional liquid for the collecting operation to the collector and discharge the liquid after the collecting operation from the collector. The particle counter measures the number of particles contained in the liquid discharged from the collector with the series of liquid input/output operations.