A transmission wave corresponding to an FM continuous wave having been subjected to an FM modulation processing is transmitted from a transmitting transducer. A pre-amplifier generates a reception RF signal and outputs the reception RF signal to a receiving mixer. The receiving mixer applies orthogonal detection to the reception RF signal to generate a complex signal. A reference signal supplied to each mixer in the receiving mixer is generated based on an FM continuous wave output from an FM modulator. The FM continuous wave output from the FM modulator is delayed by a delay circuit, and one signal is directly supplied to a mixer whereas the other signal is supplied to a mixer via a π/2 shift circuit. The delay circuit applies a delay processing in accordance with a depth of a target position within a living organism to the FM continuous wave.
