The flowmeter is provided with an oscillation circuit receiving supply of electric power in a non-insulated manner from an external power source and supplying the electric power to the coil to drive the magnetic substance, an insulating unit for insulating the coil from the magnetic substance and/or the electrically conductive fluid pipe, and a shielding unit being short-circuited to have a stable electric potential relative to the external power source and shielding the coil against the magnetic substance and the fluid pipe.