A piston type pump motor in which each cylinder bore is inclined with respect to the axis of an output/input shaft with a base portion of each piston fitted swingably in the corresponding cylinder bore, in order to increase the volume of each cylinder chamber without increasing the diameters of each cylinder bore and its pitch circle. In this piston type pump motor, the axes (7') of cylinder bores (7) are inclined with respect to the axis (5') of an output/input shaft (5) so as to diverge radially toward a cam plate (13).
