A signal is outputted via a transmission path with little attenuation while eliminating high-frequency noise. A current sensor includes: a coil wound around a magnetic core through whose interior a measured electrical path is inserted, is connected to ground at one end, and outputs a current with a current value in keeping with a current value of a measured current flowing on the measured electrical path; a constant impedance filter whose input terminal is connected to another end of the coil, limits a frequency range of the current inputted from the input terminal to a desired frequency range, and outputs the detection current from an output terminal; a transmission path that is directly connected at one end to the output terminal; and a terminating resistance that is connected between another end of the transmission path and ground and converts the current flowing via the transmission path to a detection voltage.