Abstract: A rotational hydraulic transformer for boosting system pressure of a hydraulic system, which is continuous, compact and has little pulsation, comprises: a first volume increasing/decreasing mechanism Y1 for cyclically and continuously increasing/decreasing the volume of a plurality of first annularly arranged spaces 8, by shifting the phase of each, by means of employing relative positional change of two relative moving members 1 and 3; a second volume increasing/decreasing mechanism Y2 for cyclically and continuously increasing/decreasing the volume of a plurality of second annularly arranged spaces, by shifting the phase of each, the second volume increasing/decreasing mechanism Y2 sharing the two relative moving members 1 and 3, and performing the increasing/decreasing by means of employing relative positional change of the two relative moving members; a pair of first channels A01 and A02, wherein one channel is connected to said first spaces of which the volume is increasing while the other channel is con