An ultrasonic Doppler diagnosis device having a velocity data interpolating section for generating interpolated velocity data for interpolating velocity data between two sound lines and two scanning lines, using the velocity data at the intersections. The velocity data interpolating section converts two scalar arrays of unsigned numeric data corresponding to a first and second numeric values to signed arrays of numeric data using a data converting section and generates the interpolated velocity data based on the converted signed array of numeric data, when a result of identification obtained from an identifying section indicates that one of the first and second numeric values has a positive velocity smaller than a first threshold value corresponding to a positive velocity, and the other of the first and second numeric values has a negative velocity greater than a second threshold value corresponding to a negative velocity.