A brake cylinder device comprising: a parking spring brake mechanism for parking a vehicle, wherein a first piston installed in a first cylinder section travels in a predetermined braking direction due to a biasing force of a first spring installed in the first cylinder section; a brake output section capable of advancing and withdrawing along a direction intersecting the braking direction; a brake force transmitting section having an inclined surface inclined so as to press the brake output section in an advancement direction by traveling in the braking direction along with the first piston, wherein the inclined surface includes a first inclined surface provided in a distal end portion of the brake force transmitting section, and a second inclined surface provided in a proximal end portion of the brake force transmitting section and inclined more than the first inclined surface with respect to the advancement direction, characterized in that it further comprises a fluid brake mechanism wherein a second piston installed in a second cylinder section travels in the braking direction; and a transmission mechanism configured to transmit a biasing force of the first piston in the braking direction to the second piston or a shaft section to be displaced along with the second piston, wherein the fluid brake mechanism includes an internal cylinder member having a cylindrical shape, the internal cylinder member is formed of a member separate from the second cylinder section and contained in the second cylinder section, and the second piston slides on an inner circumferential surface of the internal cylinder member. a parking spring brake mechanism for parking a vehicle, wherein a first piston installed in a first cylinder section travels in a predetermined braking direction due to a biasing force of a first spring installed in the first cylinder section; a brake output section capable of advancing and withdrawing along a direction intersecting the braking direction; a brake force transmitting section having an inclined surface inclined so as to press the brake output section in an advancement direction by traveling in the braking direction along with the first piston, wherein the inclined surface includes a first inclined surface provided in a distal end portion of the brake force transmitting section, and a second inclined surface provided in a proximal end portion of the brake force transmitting section and inclined more than the first inclined surface with respect to the advancement direction, characterized in that it further comprises a fluid brake mechanism wherein a second piston installed in a second cylinder section travels in the braking direction; and a transmission mechanism configured to transmit a biasing force of the first piston in the braking direction to the second piston or a shaft section to be displaced along with the second piston, wherein the fluid brake mechanism includes an internal cylinder member having a cylindrical shape, the internal cylinder member is formed of a member separate from the second cylinder section and contained in the second cylinder section, and the second piston slides on an inner circumferential surface of the internal cylinder member.