There is offered a water meter that requires no coil so that its cost is reduced. The water meter is formed to include an impeller, a rotation reduction unit, a first circular plate, a second circular plate, a rotation detection unit and an arithmetic unit. The rotation detection unit forms first, second and third combination capacitors with a switching circuit. The rotation detection unit detects changes in capacitances of the first, second and third combination capacitors associated with a rotation of the first circular plate. The arithmetic unit is configured so as to electrically detect the rotation angle θ of the first circular plate based on the changes in the capacitances.