An ultrasonograph capable of generating a transmission beam having a uniform width over a wide range in an ultrasonic wave propagation direction is provided. A weighted mean value of a plurality of transmission delay time values corresponding to focal lengths of transmission pulse waves set in the ultrasonic wave propagation direction is calculated for each element constituting a transmission aperture and used as the delay time for the element when waves are transmitted. As the weight used for obtaining the weighted mean value, a transmission effective aperture width according to each transmission focal length is selected, and a weight in the direction of the transmit aperture realizing the width is calculated and is used in a focal length direction.