Abstract: An intra-observation apparatus comprises an endoscope inserted into the blood vessel, a television camera for converting to an image signal an image which is obtained from the distal end of the endoscope, an endoscopic image analyzer for determining the state of observation at a region of interest on the basis of the image signal and an injector device for controlling the level of an injection flow into the blood vessel in accordance with the state of observation at the region of interest. The analyzer determines an occupation area of the blood level on the observation image and the injector device injects into the blood vessel the injection flow level of the liquid in accordance with the blood level.