To provide a reversible flowmeter which can measure the flow rate of a fluid in both normal and reverse directions with one flowmeter so as to reduce the piping space of a water treatment device, etc.

A reversible flowmeter is provided with an orifice 20 for both normal and reverse directions which is inserted into a pipeline 10, a pair of measuring pipelines 31 and 32 which are respectively led out from the front and rear sides of the office 20, a flowmeter 60, and a flow passage switching mechanism 40 which connects the pipelines 31 and 32 to the flowmeter 60 in the forward direction. The mechanism 40 is constituted of four check valves 41-44.