Abstract: An internal gear pump motor having a housing, a pinion and an internal gear rotatably supported in the housing and meshing with each other, and filler piece means located in a space defined between the pinion and internal gear for dividing the space into two regions providing a low pressure region and a high pressure region during operation. The filler piece means includes at least one filler piece floatingly mounted within the space and having portions capable of coming into sliding engagement with tooth crests of the pinion and internal gear respectively in a portion of the space where the distance between the tooth crests of the pinion and internal gear is reduced toward the low pressure region. A stopper pin is secured to the housing operative to engage one end of the filler piece on the side of the low pressure region for restricting the circumferential movement of the filler piece toward the low pressure region.