An ultrasound signal processing device includes: a receiver acquiring a receive signal sequence based on reflected detection waves received in time sequence from a subject, to generate receive signal frame data in a first orthogonal space (time direction and azimuth direction)； an orthogonal space transform unit transforming the receive signal frame data to a second orthogonal space, to generate observed spectrum frame data； a transform processor processing observed spectrum partial frame data corresponding to a partial region in the second orthogonal space of the observed spectrum frame data, to generate transformed spectrum partial frame data in a third orthogonal space； and an orthogonal space inverse transform unit performing an inverse orthogonal transform on the transformed spectrum partial frame data to an orthogonal space (subject depth direction and the azimuth direction), to generate acoustic line signals for observation points in a region of interest, to generate acoustic line signal frame data.
