A flowmeter for measuring a flow quantity of a fluid using a detection result of a state detector (12a, 12b), comprising: an exciting coil configured to apply a magnetic field to the fluid which is a measurement target; an insulator which is used for insulating the exciting coil; the state detector (12a, 12b) configured to detect an electromotive force in the fluid which is generated by the applied magnetic field; a driver configured to supply an exciting current for driving the exciting coil; a first current detecting resistance that is disposed between the exciting coil and the driver, the first current detecting resistance being configured to detect the exciting current; and a processor configured to diagnose insulation deterioration of the exciting coil in accordance with a change of a detection result of the first current detecting resistance, characterized in that wherein the driver comprises a second current detecting resistance connected to the first current detecting resistance, wherein a connecting point between the first current detecting resistance and the second current detecting resistance is connected to a ground, said flowmeter further being characterized in that the insulator is connected to the ground, the processor stores a threshold for diagnosing the exciting coil, wherein in a case that the insulation deterioration of the exciting coil occurs, a part of the exciting current does not flow through the first current detecting resistance but flows from the deteriorated insulator through the ground to the second current detecting resistance, and wherein in a case that a difference between the detection result of the first current detecting resistance and a detection result of the second current detecting resistance exceeds the threshold, the processor is configured to diagnose that the insulation deterioration of the exciting coil occurs. an exciting coil configured to apply a magnetic field to the fluid which is a measurement target; an insulator which is used for insulating the exciting coil; the state detector (12a, 12b) configured to detect an electromotive force in the fluid which is generated by the applied magnetic field; a driver configured to supply an exciting current for driving the exciting coil; a first current detecting resistance that is disposed between the exciting coil and the driver, the first current detecting resistance being configured to detect the exciting current; and a processor configured to diagnose insulation deterioration of the exciting coil in accordance with a change of a detection result of the first current detecting resistance, characterized in that wherein the driver comprises a second current detecting resistance connected to the first current detecting resistance, wherein a connecting point between the first current detecting resistance and the second current detecting resistance is connected to a ground, said flowmeter further being characterized in that the insulator is connected to the ground, the processor stores a threshold for diagnosing the exciting coil, wherein in a case that the insulation deterioration of the exciting coil occurs, a part of the exciting current does not flow through the first current detecting resistance but flows from the deteriorated insulator through the ground to the second current detecting resistance, and wherein in a case that a difference between the detection result of the first current detecting resistance and a detection result of the second current detecting resistance exceeds the threshold, the processor is configured to diagnose that the insulation deterioration of the exciting coil occurs.