[Objective]To obtain ambient sound velocity of a subject with high accuracy in a ultrasonic diagnosis apparatus.[Constitution]In an ambient sound velocity obtaining method that transmits ultrasonic waves from an ultrasonic probe, receives reflected waves reflected by a subject to obtain received signals, performs a receive focusing process on the received signals using receive delay times based on a plurality of sound velocity settings to obtain in-phase sum signals with respect to each sound velocity setting, and obtains an ambient sound velocity of the subject based on the in-phase sum signals with respect to each sound velocity setting, the in-phase sum signals with respect to each sound velocity setting is separated into an in-phase sum signal corresponding to a boundary portion in the subject and an in-phase sum signal corresponding to portions other than the boundary portion, an index is obtained based on at least either one of the in-phase sum signals, and the ambient sound velocity is obtained based on the index.
