1. An ultrasonic diagnostic apparatus comprising: an ultrasonic probe for transmitting ultrasonic waves to an object to be inspected and receiving ultrasonic echoes generated by reflection of the ultrasonic waves in the object to output reception signals; a signal processing unit for performing at least envelope detection processing on the reception signals outputted from said ultrasonic probe to generate envelope data; an image data generating unit for generating image data representing an ultrasonic image on the object based on the envelope data; a pre-measurement processing part for performing structural image generating processing on the envelope data; an operation unit to be used for presetting plural combination patterns of measurement points to be extracted to measure a distance between a first peak, which appears when ultrasonic waves are reflected at a boundary between a vascular lumen and an intima, and a second peak, which appears when ultrasonic waves are reflected at a boundary between a media and an adventitia, from among local minimum points, local maximum points, and midpoints between the local minimum points and the local maximum points of the envelope data, and for presetting priorities of the plural combination patterns; and a measurement part for extracting a pair of measurement points from the envelope data processed by said pre-measurement processing part according to a combination pattern of measurement points selected from among the plural combination patterns of measurement points in order of the priorities of the plural combination patterns, and measuring an IMT (intima media thickness) of a blood vessel based on coordinates of the extracted pair of measurement points.