A light scattering particle counter that improves the signal-to-noise ratio by attenuating the high frequency noise component while suppressing the attenuation of the signal component by irradiating a sample fluid with a laser beam La to form a particle detection area, detecting a particle with a multi-channel light detecting element that receives scattered light Ls from a particle passing through the particle detection area, and with low pass filters having time constants τc, τm, τe that are set to depend on beam diameter of the laser beam La and flow velocity of the fluid which flows through each divided area, to count particles in the sample fluid.