The present disclosure increases the braking force of a parking spring brake mechanism without enlarging a device and without substantial increase in cost. The subject of the present disclosure is a brake cylinder device provided with a parking spring brake mechanism wherein a first piston moves in a prescribed braking direction. The brake cylinder device is provided with a brake force transmitting section having an inclined surface 38 that is inclined so as to press a brake output section in an advancement direction by moving along with the first piston in the braking direction. The inclined surface includes a first inclined surface provided in a distal end portion, and a second inclined surface provided in a proximal end portion and inclined more than the first inclined surface with respect to the advancement direction.