A brake cylinder device comprising: a parking spring brake mechanism activated when parking a vehicle, wherein the parking spring brake mechanism includes a cylinder, a piston accommodated in the cylinder, and a parking spring that biases the piston so that the piston moves in a brake actuation direction; a brake force transmission that transmits the biasing force of the piston to a brake output portion (11, 61), which pushes a pushed portion of a braking subject; a clutch mechanism (27, 77) configured to transmit the biasing force of the piston to the brake force transmission or interrupt the transmission of the biasing force of the piston to the brake force transmission; a latch member configured so that a distal end of the latch member is engaged with the clutch mechanism (27, 77) when the latch member is in an advanced state advanced toward the clutch mechanism (27, 77) and so that the distal end is disengaged from the clutch mechanism (27, 77) when the latch member is in a retracted state retracted from the clutch mechanism (27, 77), wherein the latch member restricts displacement of the brake force transmission relative to the piston in the advanced state when the parking spring brake mechanism is activated and permits displacement of the brake force transmission relative to the piston in the retracted state when the parking spring brake mechanism is activated; a latch lock member that includes an inclined portion arranged to contact a distal end of a projection formed on the latch member projecting in an advancing direction of the latch member, wherein the latch lock member advances in the brake actuation direction when the latch member shifts to the retracted state and pushes the latch member in a retracting direction of the latch member with the inclined portion; a guide portion that guides the latch lock member and allows the latch lock member to advance and retract; characterised by a rotation restriction portion that restricts rotation of the latch lock member about the advancing/retracting direction of the latch lock member relative to the guide portion. a parking spring brake mechanism activated when parking a vehicle, wherein the parking spring brake mechanism includes a cylinder, a piston accommodated in the cylinder, and a parking spring that biases the piston so that the piston moves in a brake actuation direction; a brake force transmission that transmits the biasing force of the piston to a brake output portion (11, 61), which pushes a pushed portion of a braking subject; a clutch mechanism (27, 77) configured to transmit the biasing force of the piston to the brake force transmission or interrupt the transmission of the biasing force of the piston to the brake force transmission; a latch member configured so that a distal end of the latch member is engaged with the clutch mechanism (27, 77) when the latch member is in an advanced state advanced toward the clutch mechanism (27, 77) and so that the distal end is disengaged from the clutch mechanism (27, 77) when the latch member is in a retracted state retracted from the clutch mechanism (27, 77), wherein the latch member restricts displacement of the brake force transmission relative to the piston in the advanced state when the parking spring brake mechanism is activated and permits displacement of the brake force transmission relative to the piston in the retracted state when the parking spring brake mechanism is activated; a latch lock member that includes an inclined portion arranged to contact a distal end of a projection formed on the latch member projecting in an advancing direction of the latch member, wherein the latch lock member advances in the brake actuation direction when the latch member shifts to the retracted state and pushes the latch member in a retracting direction of the latch member with the inclined portion; a guide portion that guides the latch lock member and allows the latch lock member to advance and retract; characterised by a rotation restriction portion that restricts rotation of the latch lock member about the advancing/retracting direction of the latch lock member relative to the guide portion.