Phased signals of multiple channels are added without sampling clocks of multiple phases, and the limit to the frequency of a reference wave is reduced even at a constant sampling rate. The multichannel digital receiving device comprises a probe (2) which receives ultrasonic echo signals and outputs analog reception signals through multiple channels, A/D converters (31-3x), delay circuits (41-4x) which are respectively provided for the channels and delay digital data by prescribed delay time, digital quadrature detecting circuits (61-6x) which perform digital quadrature detection of delayed digital data and extract channel in-phase components and channel quadrature components, an adder circuit (71) which adds the channel in-phase components and outputs a synthesized in-phase component, and another adder circuit (7Q) which adds the channel quadrature components and outputs a synthesized quadrature component (7Q).