A blood flow sensor which continuously and non-invasively measures the peripheral blood flow of an artery was made and examined. This system uses similar effect used in conventional electro-magnetic blood flow sensor which pinchs an artery pulled out invasively by a couple of magnetic poles and electrodes and measure voltage induced on the surface of vessel by the applied magnetic field. Our system applies magnetic field from the outside of a body to the artery and measures the voltage induced on the surface of the vessel by the blood flow. This suggests capability of non-invasive and continuous measurement of blood flow. The wave forms was compared to the wave form earned by ultrasonic Doppler effect and was found to be very similar the wave form by ultrasonic Doppler system. But the signal level which was thought to be determined by blood flow, magnetic field and distribution of electric field in the body is very complicated compared with a conventional method. It is very difficult to speculate the value of blood flow precisely. But we can see the comparative change of blood flow. We got optimum condition of this method by simulation and model test. We had the blood flow signal of radial artery with high S/N ratio by this system, which shows high usability of this system for clinical use such as blood flow monitoring during an operation and before and after rehabilitation training.