A blooming measuring method for solid state image pick-up device and an apparatus thereof are disclosed, the method being constituted such that a spot beam having a certain area is irradiated to the light receiving zone of the solid state image pick-up device; the number of high level signal charges are counted from among the signal charges which are outputted from the solid state image pick-up device, and which are corresponding to one picture; and the counted value is compared with the area of the above mentioned spot beam. The apparatus of the present invention comprises: a light ray supplying means for supplying a spot beam; a driving signal generating means for driving the solid state image pick-up device; a signal detecting means for detecting only the signal charges; and a counting means for counting only the high level signals. According to the present invention, the variations of the characteristics can be excluded, and the measured results are outputted in a quantitative form, thereby making it possible to understand the characteristics exactly and precisely.