To miniaturize a torque converter by setting the fitting position of a balance piece to be on the outer circumferential side than a top part of a curved surface of an impeller shell, and at the position in the radial direction further than the outermost diameter position of a converter cover, and at a part except an embossed part.

In an outer surface of an impeller shell 2 in which an outer circumferential part of a torque converter TC is connected to a converter cover 1, a balance piece 6 is mounted on a part closer to the converter cover 1 than to a top part 2a of a curved surface, and at the position between an end part in the outermost direction of the impeller shell 2 and an end part in the outermost direction of an impeller blade 4. When the mounting position is set like this, the outermost diameter of the torque converter TC is the position R of an outer circumferential surface of the converter cover 1, and the balance piece 6 avoids increase in size of the torque converter TC. The capacity of the torque converter TC and rigidity of a differential 8 can be compatibly and easily secured.