An ultrasonic probe according to the present invention includes: an ultrasonic element for transmitting and receiving an ultrasonic signal; a signal line for transmitting an electric signal to or from the ultrasonic element; and a ground line for supplying a ground potential to the ultrasonic element. The ultrasonic element is connected electrically with a sensor signal substrate and a sensor ground substrate. These substrates are connected electrically with the signal line and the ground line, respectively, via a cable substrate. The sensor ground substrate and the cable substrate are connected directly or via a relay ground substrate.