A brake device includes: a mechanical pressure regulating part having a high-pressure port, a low-pressure port, a pilot pressure input port, and an output port which outputs fluid pressure corresponding to the pressure supplied to the pilot pressure input port by fluid pressures supplied to both of the high- and low-pressure ports, to a chamber for a master piston; a high-pressure source connected to the high-pressure port and the pilot pressure input port; a low-pressure source connected to the low-pressure port and the pilot pressure input port; and an electrically-operated pilot pressure generating part which includes control valves for controlling flows of the brake fluid between the high-pressure source and the pilot pressure input port, and between the low-pressure source and the pilot pressure input port, respectively, and which outputs desired fluid pressure to the pilot pressure input port by controlling flow of the brake fluid with control valves.