To increase a degree of freedom of setting a position for arranging pump body part and pump driving part when arranging the pump driving part outside a hydraulic fluid by immersing the pump body part in the hydraulic fluid.

This hydraulically driven pump has the pump body part 3 arranged inside the hydraulic fluid stored in a vessel C and the pump driving part 2 arranged outside the hydraulic fluid, and the pump driving part 2 forcibly sends the hydraulic fluid by driving the pump body part 3 via hydraulic pressure transmitted via a hydraulic pressure transmitting pipe 4. The pump body part 3 has a pair of pump elements 31, and the respective pump elements 31 have a pump chamber 38 partitioned by a cylindrical flexible film 37, a suction valve 34 and a delivery valve 36 continuing with the pump chamber 38 and a hydraulic pressure chamber 39 arranged outside the pump chamber 38 so as to face to the flexible film 37. The pump driving part 2 has a pair of plungers 13 actuated by a swash plate 16 rotatably driven by a driving source 14, and the hydraulic pressure generated by the respective plungers 13 is transmitted to the hydraulic pressure chamber 39 of the corresponding pump elements 31.