member 7 are described below in detail the first acoustic matching layer 5 fills a space surrounding the conductor 4 in general an acoustic impedance of the conductor 4 does not correspond to an acoustic impedance of the first acoustic matching layer 5 hence an acoustic characteristic varies depending on whether provided directly below the electromechanical transducer element 2 is the first acoustic matching layer 5 or the conductor 4 the area occupied by the conductor 4 is desirably decreased to equalize acoustic characteristics of the electromechanical transducer elements 2 however if the acoustic impedance of the conductor 4 is larger than an acoustic impedance of the substrate 1 the ultrasonic wave transmitted to the electric wiring substrate 3 is reduced and also transmission of the ultrasonic wave reflected by the electric wiring substrate 3 to the substrate 1 is reduced if the substrate 1 is made of silicon and the conductor 4 is made of typical lead free solder the above relationship is applied the influence of the reflection wave to the electromechanical transducer element 2 on the conductor 4 is small a plurality of the conductors 4 is provided on the back surface of the substrate 1 by at least a number corresponding to the number of electromechanical transducer elements 2 to electrically separate the two dimensionally arrayed electromechanical transducer elements 2 hence part of a space between the substrate 1 and the electric wiring substrate 3 not occupied by the conductors 4 is filled with the first acoustic matching layer 5 the acoustic impedance of the first acoustic matching layer 5 is designed to be a value between the acoustic impedance of the substrate 1 and an acoustic impedance of the.