Ultrasonic flowmeter and fluid controller having the same

An ultrasonic flowmeter comprising a measurement pipe through which a fluid flows, and two ultrasonic transceivers mounted on two transmitting bodies, respectively, said transmitting bodies being provided on outer side portions of the measurement pipe so as to be spaced from each other in an axis direction, said measurement pipe and said two transmitting bodies being formed integrally with each other, said ultrasonic flowmeter determining a flow velocity of the fluid by receiving an ultrasonic vibration transmitted from one of said two ultrasonic transceivers through the fluid in said measurement pipe with the other ultrasonic transceiver, alternately switching between the ultrasonic transceiver on the transmitting side and the ultrasonic transceiver on the receiving side, and measuring the ultrasonic propagation time between said two ultrasonic transceivers,

• wherein said measurement pipe has a length, an inner diameter uniform in a length direction, and an arithmetic mean roughness Ra of an inner peripheral surface, said inner diameter being equal to or less than 5 mm, said length of said measurement pipe being equal to or more than 30 mm, and said arithmetic mean roughness Ra satisfying a relation of 0 μm<Ra≦0.2 μm.