An ultrasonic diagnosis apparatus for obtaining an ultrasonic echo image upon transmission/reception of a focussed ultrasonic beam by using an ultrasonic probe having curved array transducer elements disposed in a convexity. As the delay distribution data to be used for focussing respective transducer elements, a plurality of sets of delay distribution data, each set corresponding to a particular thickness of a fat layer under a skin of a specimen, are stored in a memory. In imaging the specimen, a set of the plurality of sets of delay distribution data is selected and read in accordance with the thickness of the fat layer of the specimen to control the delay distribution of a transmission or reception signal for respective transducer elements to thereby eliminate focussing errors to be caused by the concave lens effect of the fat layer.