Disclosed is a flow imaging cytometer having a flow cell one side of which is irradiated with excitation light, in which wavelength selecting means for reflecting excitation light and transmitting fluorescence or reflecting means for reflecting excitation light is provided on the side of the flow cell opposite the side irradiated, thereby increasing the intensity of the excitation light so that the intensity of fluorescence emitted from an irradiated cell is increased. It is possible to pick up the fluorescent images at all times. The cytometer includes a light source for emitting the excitation light, dichroic mirrors which construct the wavelength selecting means, a photomultiplier for detecting fluorescence from irradiated cells, and a cell flow-by decision circuit which, based upon a detection signal from the photomultiplier, determines whether a detected cell of interest is suited to pick-up of a fluorescent image and produces a prescribed control signal for controlling an electronic shutter.
Flow imaging cytometer