To provide an ultrasonograph capable of generating a transmission beam comprising a main beam having a uniform width over a wide range in an ultrasonic wave propagation direction by one-time transmission of an ultrasonic pulse. A weighted mean value of a plurality of transmission delay time values corresponding to focal lengths of transmission pulse waves having a plurality of focal points which are set in the ultrasonic wave propagation direction is calculated for each of elements constituting a transmission aperture and used as the delay time. Waves are actually transmitted with the weighted mean value as delay time. As the weight used for obtaining the delay time mean value, first, 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. As a result, the curvature of a wave front of a wave transmitted is close to that of the wave front of a short focal length in the center portion of the transmit aperture, and is close to that of the wave front of a long focal length in the peripheral portion. Consequently, a non-cylindrical wave front is formed. Thus, a transmission beam including a relatively narrow main beam with a uniform width over a wide range in the ultrasonic wave propagation direction can be generated by one-time transmission of an ultrasonic pulse. <；IMAGE>；
