Flowmeter

A flowmeter inserted into, and fixed to, a main passage through which a target fluid flows, the flowmeter being configured to measure a flow rate of the target fluid in the main passage, the flowmeter comprising:

• a housing including:
• a side surface that extends in an insertion direction of the flowmeter;
• and
• a tip end surface that is located on a side of the side surface in the insertion direction;
• a sub passage that is defined in the housing, a part of the target fluid flowing into the sub passage from the main passage;
• an inlet portion that is defined in the side surface, the target fluid flowing into the sub passage through the inlet portion from the main passage;
• an outlet portion through which the target fluid flows out of the sub passage into the main passage;
• a flow rate detector that is configured to detect the flow rate of the target fluid flowing through the sub passage;
• and
• a protrusion that protrudes from the tip end surface in the insertion direction, wherein
• the tip end surface includes a first end area located close to the inlet portion and a second end area opposite to the first end area,
• the protrusion is located in both the first end area and the second end area;
• and
• the protrusion includes a plurality of protrusion elements that are disposed in the first end area and the second end area.