Described herein is an ultrasound internal examination system which essentially includes: an ultrasound probe having an ultrasound vibratory element at the tip end of a flexible cable to be passed through a biopsy channel of an endoscope; an operating unit detachably mounted at the rear end of the biopsy channel of the endoscope and connected to a base end portion of the flexible cable; a probe operating member provided on the operating unit to scan the ultrasound vibratory member over a predetermined scanning range; an initial position sensor means for detecting the position of an initial point of the scanning range; and an incremental encoder adapted to generate pulse signals at a predetermined frequency upon detection of and during a displacement of the ultrasound vibratory element caused by the probe operating member.
