To provide a radial piston pump capable of suppressing the upsizing of the outer and inner peripheral side members in a radial direction.

A radial piston pump which is provided with an outer peripheral side member 3 and inner peripheral side member 5 relatively rotatable around an axial line A1, a cam surface 20 provided to the outer peripheral side member 3, a piston 7 provided to the inner peripheral side member 5 and movable in a radial direction, and a fluid chamber 9 provided to the inner peripheral side member 5, and has a configuration allowing the change in a capacity of fluid sucked into/discharged from the fluid chamber 9. The axial line A1 intersects with the center line B1 of a cam surface within a plane in a direction along the axial line A1, and includes a capacity adjustment mechanism 21 for changing the capacity of fluid sucked into/discharged from the fluid chamber 9 by relatively moving the outer peripheral side member 3 and inner peripheral side member 5 in a direction along the axial line A1.