The influence of noise included in the Doppler signal can be reliably reduced without complicated calculation processing and an increase in memory consumption, and a high-quality color Doppler image can be obtained even when the folding speed is exceeded. The filtering unit 85 of the ultrasonic diagnostic apparatus 1 includes a central processing unit 87 and an input control unit 86. The input control unit 86 includes a sign extension unit 91, a quadrant transition determination unit 92, a filter coefficient switching unit 93, and a phase offset unit 94. The sign extension unit 91 extends the upper bits to obtain an extended Doppler signal. The quadrant transition determination unit 92 performs phase angle transition determination based on the extended Doppler signal and the immediately preceding extended Doppler signal. The filter coefficient switching unit 93 decreases the filter coefficient when transitioning from the first to third quadrant and transition from the fourth to second quadrant. The phase offset unit 94 adds or subtracts the phase corresponding to π to the phase value in the extended Doppler signal when transitioning between the second and third quadrants. Selection diagram: Fig. 5複雑な演算処理やメモリ消費量の増大を伴わず、ドプラ信号に含まれるノイズの影響を確実に低減でき、折り返り速度を超えても良質なカラードプラ画像を得る。超音波診断装置１のフィルタリング手段８５は、中央処理部８７、入力制御部８６を備える。入力制御部８６は、符号拡張部９１、象限推移判定部９２、フィルタ係数切換部９３、位相オフセット部９４を有する。符号拡張部９１は上位ビットを拡張して拡張ドプラ信号とする。象限推移判定部９２は、拡張ドプラ信号と直前の拡張ドプラ信号とに基づき位相角の推移判定を行う。フィルタ係数切換部９３は、第１→第３象限への推移、第４→第２象限への推移のときにフィルタ係数を小さくする。位相オフセット部９４は、第２－第３象限間での推移のときに、拡張ドプラ信号における位相の値にπに相当する位相分を加算または減算する。選択図：図５
