A flowmeter includes an exciter configured to excite fluid which is a measurement target, a state detector configured to detect a state of the fluid excited by the exciter, a driver configured to supply exciting current for driving the exciter, a first current detector that is disposed between the exciter and the driver, the first current detector being configured to detect the exciting current, and a processor configured to diagnose insulation deterioration of the exciter in accordance with a change of a detection result of the first current detector.