A flowmeter is disposed in a passage through which a fluid flows. The flowmeter includes a first passage and a second passage. The first passage defines an opening through which a part of the fluid flows into the flowmeter from the passage. The second passage branches off from the first passage and includes a flow rate detector configured to detect a flow rate of the fluid flowing through the second passage from the first passage. The second passage has one end at which the second passage branches off from the first passage and the other end. The second passage includes at least one end opening at the other end and an inflow reducer configured to restrict the fluid from flowing into the second passage through the at least one end opening.