A particle counter includes: a multi-flow cell with flow passages arrayed in a first direction and having a section including a detection region, for detecting a particle, formed when the flow passage is irradiated with irradiation light; a light receiving optical system configured to receive emitted light generated from a particle contained in sample fluid flowing in the at least one flow passage and passing through the detection region; an optical axis moving unit configured to move an optical axis of the irradiation light and an optical axis of the emitted light in the first direction; and a counter configured to count the particle for each particle size based on an intensity of the emitted light.