In a torque converter for performing torque transmission by circulating a working fluid between a pump impeller and a turbine runner, the working fluid is a magnetic viscous fluid; and in a torque converter housing, outside a circulation path of the working fluid, a yoke member connected to the pump impeller and provided with a coil and a magnetic member connected to the turbine runner are concentrically arranged with a predetermined space therebetween; and a magnetic circuit is established between the yoke member and the magnetic member upon energization of the coil.