The present invention relates to a method of removing an effect of side lobes in an ultrasound synthetic image. The method includes: a) setting a plurality of scan lines and defining sequential indices upon the scan lines b) setting a transmit order of a transmit beam for the scan lines in a non-sequential manner in which increment and decrement of the indices of the scan lines are repeated c) transmitting the transmit beam based on the set transmit order to obtain a plurality of receive beams in response to each transmission of the transmit beam d) grouping the receive beams to an increment group corresponding to an increment direction of the numbers of the scan lines and a decrement group corresponding to a decrement direction of the numbers of the scan lines e) performing an auto correlation upon the receive beams included in the respective increment group and the decrement group and f) applying weights to the auto correlation results and summing the weight-applied auto correlation results to thereby remove an effect of side lobes.
