A treatment instrument includes a power receiver and a treatment section configured to be driven by power received by the power receiver. The power receiver includes a first solenoid-shaped power receiving coil and a second solenoid-shaped power receiving coil having a winding direction opposite to a winding direction of the first power receiving coil. The first power receiving coil and the second power receiving coil have the same length and the same number of turns, and are arranged concentrically. The first power receiving coil and the second power receiving coil are electrically connected to a treatment section so that a direction in which a current flows through the first power receiving coil is opposite to a direction in which a current flows through the second power receiving coil.