A gas flowmeter includes: a device body which air-tightly accommodates a fluid to be measured; an inlet pipe through which the fluid to be measured is made to flow into the device body; and an outlet pipe through which the fluid to be measured is made to flow out from the device body. The gas flowmeter further includes: an ultrasonic flow rate measuring unit which is connected to the outlet pipe and measures a flow rate of the fluid to be measured which flows in the ultrasonic flow rate measuring unit; a connecting pipe which is connected to the outlet pipe; and a flow passage member which is connected to the connecting pipe and has a flow passage shape identical to a shape of the ultrasonic flow rate measuring unit. The gas flowmeter is provided with a support member which fixes the ultrasonic flow rate measuring unit and the flow passage member to each other. With such a configuration, a gas flow meter capable of performing stable flow rate measurement can be implemented.