To easily recognize the result of blood flow measurement and measurement condition, and observe a measurement state of a subject eye by controlling display on a display unit.

A blood vessel as a subject to be measured is decided, and a laser beam irradiation switch in an input device 48 is pushed, so that FFT signals are inputted from an FFT computing element 64 which frequency- converts received light signals from photomultipliers 45a and 45b to a data display control part 67. The data display control part 67 makes a change to display of FFT, and FFT information is displayed at a lest lower part of the display unit 50. As a laser control part 61 receives an input signal from the laser beam radiation switch, it makes irradiation of a laser beam from a tracking light source 33 and a laser diode 31. Simultaneously, it outputs an irradiation start signal S1 to an observation image control part 66, and an eyeground image from a CCD camera 19 is enlarged and displayed on the display unit 50.