PARKING BRAKE DEVICE

A parking brake system is provided in which, a lock mechanism (25) is provided within a casing (23) to the rear of a parking piston (24) that can give a parking brake state by forward movement in response to the action of a parking control fluid pressure, the lock mechanism (25) operating in response to forward movement of the parking piston (24) in order to mechanically lock the parking piston (24) at a forward position and unlocking in response to the action of a parking release control fluid pressure. The lock mechanism (25) includes a lock piston (30) that is disposed to the rear of the parking piston (24) while having an axis orthogonal to the axis of the parking piston (24) and that makes a forward urging force act on the parking piston (24) at least when the parking piston (24) moves forward, and opposite end parts of the lock piston (30) are slidably fitted into and supported on the casing (23). This enables an automatic parking brake state to be obtained by a simple structure without consuming power.