An oil pressure generator 20 includes a drive gear 30, a driven gear 32, and a crescent 34, which constitute a gear pump unit, as well as one-way clutches 36 and 38 that respectively interlock with two rotating shafts 42 and 46 when the rotating shafts 42 and 46 rotate in an identical direction relative to the drive gear 30. In case that both the rotating shafts 42 and 46 rotate in the interlocking direction, the corresponding one-way clutch interlocks with the rotating shaft having a greater revolving speed, thereby driving the drive gear 30. This structure enables the oil pressure generator 20 to produce an oil pressure through rotation of the rotating shaft having a greater revolving speed out of the two rotating shafts 42 and 46.