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 2 provided with a parking spring brake mechanism 40 wherein a first piston 43 moves in a prescribed braking direction C. The brake cylinder device 2 is provided with a brake force transmitting section 37 having an inclined surface 38 that is inclined so as to press a brake output section 7 in an advancement direction A by moving along with the first piston 43 in the braking direction C. The inclined surface 38 includes a first inclined surface 38a provided in a distal end portion, and a second inclined surface 38b provided in a proximal end portion and inclined more than the first inclined surface 38a with respect to the advancement direction A.
