To provide a hydraulic device which reduces wear and damage to a seal member by an opening on a cylinder, and a brake pressure control device using the same.

A port 514 communicating with the outside of a reservoir device 5 is opened on the inner peripheral surface 511a of a cylinder hole 511 in the reservoir device 5. A hollow part 515 is formed in a reservoir body 51 concentrically with the ports 514. An annular thin piece 516 is formed between the inner peripheral surface 511a of the cylinder hole 511 and the hollow part 515 so as to surround the port 514 in a radial direction, and is radially pressed outward with the port 514 as a center in a range narrower than an inside diameter of the hollow part 515, thereby being flexibly deformed outward. As a result, a root portion of the thin piece 516 has a curved surface in the inner peripheral surface 511a of the cylinder hole 511 while the opening 514a of the port 514 is recessed outward from the inner peripheral surface 511a of the cylinder hole 511.