PURPOSE: To measure a fluorescence attenuation time including two-dimensional position information by processing information on the incidence position of extremely weak light emission which is obtained by a two-dimensional incidence position detection tube and time information based upon reference time pulses synchronized with the excitation of fluorescence.

CONSTITUTION: A sample 1 is excited repeatedly with the exciting light of a picosecond range. A fluorescent image with light emission intensity of single-photon level which is formed by materials distributed in the sample 1 is made incident on the two-dimensional incidence position detection tube 9. The information on the incidence position of the incident fluorescence is outputted from the output terminal of a semiconductor incidence position detector 9e and information corresponding to the point of time of the incidence is outputted from the electrode of a microchannel plate 9d. The two-dimensional position signal and time signal are inputted to a data processing part 16 and recorded. The position information is sectioned into units of, for example, 3×3 picture elements and the frequency of input of a single photon at each place is integrated with a quantized time unit to obtain data on a change with the lapse of time in the extremely weak fluorescence emission of the sample corresponding to said 3×3-picture-element unit.