A brake cylinder device (2; 3) that moves a rod by operating using a pressure fluid, and outputs braking force from a brake output portion that moves along with the rod, the brake cylinder device (2; 3) comprising: a cylinder body having a hollow interior; the rod that is arranged inside the cylinder body and provided so as to be movable in a forward movement direction of moving forward from the cylinder body and in a backward movement direction of moving backward in a direction opposite to the forward movement direction, both of which are linear directions along a cylinder axial direction; a rod biasing spring capable of biasing the rod in the backward movement direction; a piston that is arranged in the cylinder body so as to define a pressure chamber and circumferentially surround an axis of the rod, is provided so as to be movable along a linear direction that is parallel to the movement direction of the rod, wherein the brake output portion is provided so as to be capable of moving along with the rod and can output braking force due to the rod moving in the forward movement direction, characterized in that the piston moves in the backward movement direction relative to the cylinder body in resistance to biasing force from the rod biasing spring due to pressure fluid being supplied to the pressure chamber; wherein the brake cylinder further comprises a force amplifying mechanism (25; 70) that, when the piston moves in the backward movement direction, moves the rod in the forward movement direction, amplifies drive force from the piston, and applies the amplified drive force to the rod; and wherein the force amplifying mechanism (25; 70) includes a swinging member (46; 73) that swings due to being biased by the piston moving in the backward movement direction, so as to bias and move the rod in the forward movement direction. a cylinder body having a hollow interior; the rod that is arranged inside the cylinder body and provided so as to be movable in a forward movement direction of moving forward from the cylinder body and in a backward movement direction of moving backward in a direction opposite to the forward movement direction, both of which are linear directions along a cylinder axial direction; a rod biasing spring capable of biasing the rod in the backward movement direction; a piston that is arranged in the cylinder body so as to define a pressure chamber and circumferentially surround an axis of the rod, is provided so as to be movable along a linear direction that is parallel to the movement direction of the rod, wherein the brake output portion is provided so as to be capable of moving along with the rod and can output braking force due to the rod moving in the forward movement direction, characterized in that the piston moves in the backward movement direction relative to the cylinder body in resistance to biasing force from the rod biasing spring due to pressure fluid being supplied to the pressure chamber; wherein the brake cylinder further comprises a force amplifying mechanism (25; 70) that, when the piston moves in the backward movement direction, moves the rod in the forward movement direction, amplifies drive force from the piston, and applies the amplified drive force to the rod; and wherein the force amplifying mechanism (25; 70) includes a swinging member (46; 73) that swings due to being biased by the piston moving in the backward movement direction, so as to bias and move the rod in the forward movement direction.