An ultrasound diagnostic apparatus configured to transmit ultrasound from an ultrasound transducer to a subject and display an ultrasound image on a monitor, the ultrasound diagnostic apparatus comprising: transducer driving means configured to transmit ultrasound with a predetermined focus position from the ultrasound transducer; display region changing means comprising a scan controller and a timing generator, the scan controller comprising a digital signal processor, a dual port RAM and a scan control section, and the timing generator comprising a flash memory, a timing generation section, and a Tx control section, wherein the Tx control section is configured to output to the transducer driving means a control signal for changing transmission timing of the ultrasound transmitted by the transducer driving means based on a timing signal from the timing generation section, according to an instruction from the scan control section, the display region changing means being configured to change a display region to be displayed on the monitor, in an ultrasound image; and control means configured to change a focus position of the ultrasound by controlling the transducer driving means according to a change result of the display region changing means, wherein the scan control section is configured to control the timing generator according to an instruction from the control means, characterized in that the control means are configured to determine a display range R in a currently executed display mode; judge whether the currently executed display mode is a full circle display mode or a half circle display mode; generate a selection signal disposing the focus position at R/4 or in the vicinity thereof and output the generated selection signal to the timing generator in case the currently executed display mode is a full circle display mode so that an ultrasound image of a full circle display is displayed in which a marker indicating the focus position is disposed at two points along one side of a display frame and at positions at 1/4 of the display range or in the vicinity thereof, and the focus position is located at the position of the marker; and generate a selection signal disposing the focus position at R/2 or in the vicinity thereof and output the generated selection signal to the timing generator in case the currently executed display mode is a half circle display mode so that an ultrasound image of a half circle display is displayed in which a marker indicating the focus position is disposed at a position of 1/2 of the display range R or in the vicinity thereof, and the focus position is located at the position of the marker. transducer driving means configured to transmit ultrasound with a predetermined focus position from the ultrasound transducer; display region changing means comprising a scan controller and a timing generator, the scan controller comprising a digital signal processor, a dual port RAM and a scan control section, and the timing generator comprising a flash memory, a timing generation section, and a Tx control section, wherein the Tx control section is configured to output to the transducer driving means a control signal for changing transmission timing of the ultrasound transmitted by the transducer driving means based on a timing signal from the timing generation section, according to an instruction from the scan control section, the display region changing means being configured to change a display region to be displayed on the monitor, in an ultrasound image; and control means configured to change a focus position of the ultrasound by controlling the transducer driving means according to a change result of the display region changing means, wherein the scan control section is configured to control the timing generator according to an instruction from the control means, characterized in that the control means are configured to determine a display range R in a currently executed display mode; judge whether the currently executed display mode is a full circle display mode or a half circle display mode; generate a selection signal disposing the focus position at R/4 or in the vicinity thereof and output the generated selection signal to the timing generator in case the currently executed display mode is a full circle display mode so that an ultrasound image of a full circle display is displayed in which a marker indicating the focus position is disposed at two points along one side of a display frame and at positions at 1/4 of the display range or in the vicinity thereof, and the focus position is located at the position of the marker; and generate a selection signal disposing the focus position at R/2 or in the vicinity thereof and output the generated selection signal to the timing generator in case the currently executed display mode is a half circle display mode so that an ultrasound image of a half circle display is displayed in which a marker indicating the focus position is disposed at a position of 1/2 of the display range R or in the vicinity thereof, and the focus position is located at the position of the marker.