A flow cytometer, in which detection of light generated from a particle is less likely to be affected by change in a flow velocity of a liquid flowing in a flow cell, is provided. The flow cytometer includes: a flow cell (10) in which a liquid flows; a liquid sending unit (40) configured to send the liquid into the flow cell (10); a controller (300) configured to obtain information related to a flow velocity of the liquid flowing in the flow cell (10); a light source (121) configured to irradiate the liquid flowing in the flow cell (10) with light; and a detector (162) configured to detect light generated from a particle in the liquid irradiated with light. The controller (300) changes a liquid sending condition for the liquid sending unit (40), based on the obtained information related to the flow velocity.

A system, method, and apparatus are provided for flow cytometry. In one example, the flow cytometry system includes dual laser devices and dual scatter channels to measure velocity of particles in a core stream of sample fluid. The total flow rate of the sample fluid and the sheath fluid around the sample fluid is controlled, and thus held constant, by a feedback control system controlling a vacuum pump based on differential pressure across ends of a flow channel in the flow cell. A stepper flow control valves are disclosed that apply a physical fluid resistance to a flow of sheath fluid in the flow cytometer. The physical fluid resistance regulates a flow rate of the sheath fluid and thereby regulates a flow rate of sample fluid in the flow cytometer.