An ultrasonic diagnostic device has an ultrasonic sensor having a substrate, a piezoelectric element mounted on the substrate for generating an ultrasonic wave to be transmitted into a living body in accordance with an input drive signal, and an intimate contact layer having a first main surface disposed in contact with the piezoelectric element and a second main surface opposite the first main surface for contacting a part of the living body. The intimate contact layer is formed of a flexible material such that the second main surface of the intimate contact layer is brought into close contact with the part of the living body so that no air gaps exist between the second main surface of the intimate contact layer and the part of the living body. A driver circuit generates an input drive signal to drive the piezoelectric element. A biological information detection portion detects biological information relating to the interior of the living body in accordance with the ultrasonic wave transmitted into the living body and an ultrasonic wave reflected from the interior of the living body. A display portion displays the biological information detected by the biological information detection portion.
