A beam former for a ultrasonic diagnostic apparatus is arranged to have low-bit analog-to-digital converters and enables to obtain an excellent echo signal from blood flow. The beam former further includes a sample and hold circuit for sampling an echo signal of a pulse reflected from the inside of a human body. A delaying circuit serves to delay the output of the sample and hold circuit by a delay time corresponding to an integer multiple of a transmitted pulse period and is subtracted from the output of the sample and hold circuit. The subtracted output is analog-to-digital converted and is stored in a memory. The memory reads out the data asynchronously with the storage. The delaying circuit is composed of an analog-to-digital converter, a memory and a digital-to-analog converter and has a delay time corresponding to an integer multiple of the transmitted pulse period.