One embodiment of the present invention is to provide a system for sorting cell particles in a liquid flow, which comprises a flow-defining block including a flow chamber receiving a sample conduit and a flow cell having a flow channel. The system also comprises a strobe block including a imaging device for taking an image of a jet flow ejected from the flow-defining block and a plurality of droplets in a given image area. The flow-defining block and the strobe block are detachably connected each other. Further the strobe block includes a nozzle plate having a nozzle channel between a receiving end and a nozzle. The flow-defining block includes a discharge end opposite to the receiving end and a channel enlarged portion of which cross section taken along a predetermined plane perpendicular to a flow direction has an area increasing towards the discharge end. The discharge end and the receiving end have substantially the same open distance in the predetermined plane perpendicular to the flow direction.