In an ultrasonic endoscope, a plurality of flexible substrates are connected to an ultrasonic probe as a signal transmission member for transmitting a signal which is inputted intooutputted from the ultrasonic probe. The first path is an impaction separation path effecting liquid particle separation from a gas-liquid stream by inertial impaction. The invention uses the existing signalling protocols to transfer further information. For the noise frequency, a corresponding noise component is determined. Each of the connecting pieces has a first side provided with at least one first linking portion and a second side provided with at least one second linking portion.