Co-based amorphous magnetic wire with a diameter of $125{mu}m$ and a length of 40 mm was used as an inner conductor of a coaxial cable to construct a magnetic sensor. Sensor characteristics was measured up to 3 GHz with applied up to 60 Oe by using network analyzer. Frequency dependence of impedance for this sensor was very close to the impedance resonant pattern of transmission line and 250 MHz was obtained as a 1/4 wavelength without external magnetic field. Large impedance change was measured in the magnetic field range between 0 Oe and 1 Oe, which was influenced by permeability change of magnetic amorphous wire. Because ${Delta}Z/{Delta}H$ value of $300{Omega}/Oe$ was obtained at 0.1 Oe, this coaxial cable with amorphous wire can be useful as a magnetic sensor.