LIGHT QUANTITY DETECTION DEVICE, AND IMMUNOANALYSIS DEVICE AND CHARGED PARTICLE BEAM DEVICE USING SAME

For a detection signal that has been detected by the photomultiplier tube 2, has been amplified by the preamplifier 5, and has been converted into a digital signal, a time average value of signal components, each of which has a voltage lower than a predetermined base threshold value, is calculated as a base voltage. Base correction processing that offsets the detection signal in such a manner that the base voltage becomes 0 is performed. A signal that has been subjected to the base correction processing is subjected to threshold value processing that calculates a signal component having a voltage higher than a predetermined signal detection threshold value, and to base correction processing in a non-incident state in which light is not incident on the photomultiplier tube 2. An output signal thereof is subjected to dark current calculation processing that calculates a signal component having a voltage higher than a predetermined signal detection threshold value. The light emission signal amount is calculated by subtracting, from the signal component of the detection light obtained by the threshold value processing, a time average value of the signal components of the dark current obtained by the dark current calculation processing. As the result, discriminating the dark current pulse from floor noises enables to enhance the accuracy of the base voltage, and thus to enhance the accuracy of light detection.