Abstract: A doppler ultrasonic flowmeter 10A includes: a Udflow unit 13 for calculating the speed of a great number of reflectors 25 contained in a fluid 12 to be measured; a flow-speed distribution calculating element 70 for calculating the flow-speed distribution of the fluid 12 to be measured within a fluid tube 11 by performing computation processing for the flow-speed data of the reflectors 25 received from the Udflow unit 13; a center position detecting element 71 for detecting the center position of the fluid tube 11; a flow-speed distribution calculating member 67 having an area selecting element 72 which allows the user to select a division area within the fluid tube 11 in units of the division area; the flow-speed distribution being calculated for the selected division area using the reflectors 25; and a flow calculating member 68 for measuring the flow by further performing computation processing for the flow-speed distribution of the fluid 12 to be measured.