An ultrasonic flow amount measuring device includes a pair of tube holding portions respectively connected to a base by a shaft portion so as to be openable and closeable, and ultrasonic transmission and reception units disposed in the tube holding portions so as to face each other in an inclined direction. When the tube holding portions are opened so as to insert a tube between holding concave portions formed in clamping portions and closed so as to clamp the tube, front end surfaces of ultrasonic transmission bodies are in close contact with both sides of a surface of the tube. When measuring a flow amount, an ultrasonic beam is alternatively transmitted and received between the ultrasonic transmission and reception units through the tube. A flow rate is obtained by obtaining a transmission time difference between the travel time and the return time of the ultrasonic beam.