An ultrasonic flowmeter comprising: a first flow rate measurement unit (10; 140; 130a) for detecting a flow rate of a fluid in a pipe by using a transit time method; a second flow rate measurement unit (20; 130; 130a) for detecting a flow rate of a fluid in the pipe by using a pulse Doppler method; a plurality of first (41; 111u; 112u, 113u) and second (42; 111d; 112d, 113d) transducer units, being mounted onto the pipe in which a fluid as the subject of measurement flows through, each of which carries out an interconversion between an acoustic signal and electric signal; and a transducer changeover unit (33; 120a; 120b; 120c) for making the first and second flow rate measurement units share the transducer unit, wherein said plurality of said first and second transducer units are mounted onto said pipe with the first and second transducer units mutually on the opposite sides across the axis of the pipe and at mutually displaced positions in the flow direction of said fluid, characterized in that said first flow rate measurement unit is adapted to measure a flow rate of the fluid by measuring the time difference between a propagation time of an acoustic signal which is transmitted from the first transducer unit and received by the second transducer unit, and a propagation time of an acoustic signal which is transmitted from the second transducer and received by the first transducer, and said second flow rate measurement unit is adapted to acquire a flow velocity profile of the entire diameter of the pipe by combining the measurement values of flow velocity profiles (51a, 51b) from the center to the pipe wall on the far side as seen from the aforementioned respective transducers from among the flow velocity profile measured by using each of the first and second transducers. a first flow rate measurement unit (10; 140; 130a) for detecting a flow rate of a fluid in a pipe by using a transit time method; a second flow rate measurement unit (20; 130; 130a) for detecting a flow rate of a fluid in the pipe by using a pulse Doppler method; a plurality of first (41; 111u; 112u, 113u) and second (42; 111d; 112d, 113d) transducer units, being mounted onto the pipe in which a fluid as the subject of measurement flows through, each of which carries out an interconversion between an acoustic signal and electric signal; and a transducer changeover unit (33; 120a; 120b; 120c) for making the first and second flow rate measurement units share the transducer unit, wherein said plurality of said first and second transducer units are mounted onto said pipe with the first and second transducer units mutually on the opposite sides across the axis of the pipe and at mutually displaced positions in the flow direction of said fluid, characterized in that said first flow rate measurement unit is adapted to measure a flow rate of the fluid by measuring the time difference between a propagation time of an acoustic signal which is transmitted from the first transducer unit and received by the second transducer unit, and a propagation time of an acoustic signal which is transmitted from the second transducer and received by the first transducer, and said second flow rate measurement unit is adapted to acquire a flow velocity profile of the entire diameter of the pipe by combining the measurement values of flow velocity profiles (51a, 51b) from the center to the pipe wall on the far side as seen from the aforementioned respective transducers from among the flow velocity profile measured by using each of the first and second transducers.