PROBLEM TO BE SOLVED: To provide a microparticle fraction collector capable of automatically detecting a deviation in orbital direction in a liquid stream or a droplet.SOLUTION: The microparticle fraction collector includes: an image pick-up device for picking up images of at least a liquid stream or a droplet flowing out from an orifice; and a control unit that controls the focus distance of the image pick-up device relative to the liquid stream or the droplet based on brightness information of the image of the liquid stream or the droplet picked up by the image pick-up device. The control unit controls the microparticle fraction collector to output an alarm to a user when a non-focus area and a focus area are identified in the image.SELECTED DRAWING: Figure 1
