PROBLEM TO BE SOLVED: To provide a gas flowmeter that enables stable flow measurement in a gas meter having an ultrasonic flow rate measuring unit and a flow channel part.SOLUTION: A gas flowmeter comprises: a device main unit 1 for air-tightly housing a fluid to be measured; an inlet pipe 4 for introducing the fluid to be measured into the device main unit 1; an outlet pipe 5 for discharging the fluid to be measured out of the device main unit 1; an ultrasonic flow rate measuring unit 9 connected to the outlet pipe 5 and calculating a flow rate of the fluid to be measured flowing inside; a connection pipe 7 connected to the outlet pipe 5; and a flow channel member connected to the connection pipe 7 and having a flow channel shape identical to that of the ultrasonic flow rate measuring unit 9. The ultrasonic flow rate measuring unit 9 and the flow channel member are downwardly connected to the connection pipe 7.