To provide an ultrasonic flowmeter equipped with a diaphragm pressure sensor suitable to be installed in an ultrasonic propagation passage of the ultrasonic flowmeter, having corrosion resistance by using a fluororesin, and its manufacturing method.

In this ultrasonic flowmeter equipped with the diaphragm pressure sensor 42 for measuring the pressure of chemical solution supplied into a chemical solution supply pipe 51 made of a fluororesin, a flow rate of the chemical solution is measured by an ultrasonic oscillation/reception parts 52A, 52B provided on both ends of the ultrasonic propagation passage 51A constituting a part of the chemical solution supply pipe under control of the pressure measured by the sensor 42. The diaphragm pressure sensor includes a diaphragm 43 formed by scraping thinly a part of a pipe wall of the chemical solution supply pipe constituting the ultrasonic propagation passage in order to form a pressure sensitive part in contact with the chemical solution, a reinforcing member 44 formed for the diaphragm, and a pressure/electricity conversion element formed for the reinforcing member.