A magnetostrictive torque sensor comprising: a columnar or tubular substrate; a first magnetostrictive portion and a second magnetostrictive portion each disposed on an outer peripheral surface of the substrate and constituted by a plating film; a first coil configured to generate a magnetic flux passing through the first magnetostrictive portion; a second coil configured to generate a magnetic flux passing through the second magnetostrictive portion and is electrically connected to the first coil in series; a first resistor disposed between the first coil and the second coil and electrically connected to the first coil and the second coil in series; a second resistor disposed between the first resistor and the second coil and electrically connected to the first resistor and the second coil in series, a detection section (48, 50) configured to detect a potential at a midpoint between the first coil and the first resistor and a potential at a midpoint between the second coil and the second resistor, a power supply section configured to supply a power supply voltage of one of a positive voltage or a negative voltage to the first coil and the second coil; and a potential generating section configured to generate an intermediate potential between a potential of the power supply voltage and a ground potential, wherein the power supply section is configured to supply the power supply voltage to the first coil and the second coil so that an alternating current flows in each of the first coil and the second coil, and the potential generating section is configured to set a potential at a midpoint between the first resistor and the second resistor at the intermediate potential. a columnar or tubular substrate; a first magnetostrictive portion and a second magnetostrictive portion each disposed on an outer peripheral surface of the substrate and constituted by a plating film; a first coil configured to generate a magnetic flux passing through the first magnetostrictive portion; a second coil configured to generate a magnetic flux passing through the second magnetostrictive portion and is electrically connected to the first coil in series; a first resistor disposed between the first coil and the second coil and electrically connected to the first coil and the second coil in series; a second resistor disposed between the first resistor and the second coil and electrically connected to the first resistor and the second coil in series, a detection section (48, 50) configured to detect a potential at a midpoint between the first coil and the first resistor and a potential at a midpoint between the second coil and the second resistor, a power supply section configured to supply a power supply voltage of one of a positive voltage or a negative voltage to the first coil and the second coil; and a potential generating section configured to generate an intermediate potential between a potential of the power supply voltage and a ground potential, wherein the power supply section is configured to supply the power supply voltage to the first coil and the second coil so that an alternating current flows in each of the first coil and the second coil, and the potential generating section is configured to set a potential at a midpoint between the first resistor and the second resistor at the intermediate potential.