A sensor element, a sensor system, a catheter that can detect the thrombi, plaques and stents in the blood vessels and manufacturing method of the sensor element are provided. A cylinder is formed as a cylinder shaped part that has a long inner space and one open end. The cylinder has a slit being formed along an axis and the width of the slit is less than diameter of the inner space. A plurality of coils is wound outside of the cylinder and the lead portions of the coils are led into the inner space of the cylinder by passing through the slits. Electrically conducting means are connected to each of lead portions and are externally led out from the open end of the cylinder.