Abstract: An ultrasonic diagnostic device comprising an ADC 60 that converts signals to digital format, a time axis extension unit 70 that is capable of writing and reading the digital data, a data compression unit 80 that compresses the read data, a memory unit 90 that stores the compressed data, a data expanding unit that expands the compressed data stored in the memory unit, and a DAC 110 that converts the expanded data from a digital format to an analog format, wherein optimum images can be displayed for diagnosis by means of filtering, logarithmically converting, and detecting before inputting the data into the digital scan converter 210.