To provide a bubble injection device capable of improving precision of a Doppler type ultrasonic flow rate meter irrespective of experience or a database.

The bubble injection device includes a flow rate meter 140, a branch channel 300 for drawing fluid from a pipe channel 200 and returning the fluid to the same, a pump 210 for transporting the fluid in the branch channel, a regulating valve 160 for regulating a flow rate or a pressure of the fluid in the branch channel, an enlarged section 230 having an enlarged inner diameter in the branch channel, a compressor 220 for supplying gas in the enlarged section 230, a regulating valve 150 for regulating a flow rate or a pressure of gas supplied from a supply section 220, and a bubble control section 180 that controls the valve 160 or the valve 150 in accordance with a bubble state measured by the flow rate meter 140.