An axle of an industrial vehicle, the axle comprising: an axle housing; a right and left pair of axle shafts inserted in the axle housing; a differential gear device arranged in the axle housing and configured to distribute power generated by a drive source to the pair of axle shafts; a power transmission device arranged outside the axle housing and configured to transmit the power to the differential gear device; and a parking brake arranged adjacent to the power transmission device outside the axle housing, the parking brake being a negative brake, the power transmission device including: a transfer housing; a transmission shaft supported rotatably around its axis by the transfer housing to transmit the power to the differential gear device; and a transmission gear mounted on the transmission shaft and rotated by the power, the parking brake including: a brake housing having an opening facing in a direction away from the axle housing, the opening being covered with a brake cover; a brake shaft supported rotatably around its axis by the brake housing; and a brake gear mounted on the brake shaft and meshed with the transmission gear, characterized in that the parking brake further includes: first brake plates attached to the brake shaft; second brake plates attached to the brake housing, the first brake plates and the second brake plates being arranged alternately in an axial direction of the brake shaft, the axle being characterised in that it further comprises a brake piston arranged in the brake housing so as to move toward and away from the first brake plates and the second brake plates in the axial direction of the brake shaft for bringing the first brake plates and the second brake plates into pressure contact with each other; and a spring arranged between the brake piston and the brake cover in the brake housing to press the brake piston against the first brake plates and the second brake plates, a brake release bolt is arranged at the center of the parking brake, penetrates the brake cover, and is screw-engaged with the brake piston, and the brake piston is moved away from the first brake plates and the second brake plates against the biasing force of the spring by rotation of the brake release bolt, and thereby the pressure contact between the first brake plates and the second brake plates is released. an axle housing; a right and left pair of axle shafts inserted in the axle housing; a differential gear device arranged in the axle housing and configured to distribute power generated by a drive source to the pair of axle shafts; a power transmission device arranged outside the axle housing and configured to transmit the power to the differential gear device; and a parking brake arranged adjacent to the power transmission device outside the axle housing, the parking brake being a negative brake, a transfer housing; a transmission shaft supported rotatably around its axis by the transfer housing to transmit the power to the differential gear device; and a transmission gear mounted on the transmission shaft and rotated by the power, a brake housing having an opening facing in a direction away from the axle housing, the opening being covered with a brake cover; a brake shaft supported rotatably around its axis by the brake housing; and a brake gear mounted on the brake shaft and meshed with the transmission gear, characterized in that first brake plates attached to the brake shaft; second brake plates attached to the brake housing, the first brake plates and the second brake plates being arranged alternately in an axial direction of the brake shaft, the axle being characterised in that it further comprises a brake piston arranged in the brake housing so as to move toward and away from the first brake plates and the second brake plates in the axial direction of the brake shaft for bringing the first brake plates and the second brake plates into pressure contact with each other; and a spring arranged between the brake piston and the brake cover in the brake housing to press the brake piston against the first brake plates and the second brake plates, a brake release bolt is arranged at the center of the parking brake, penetrates the brake cover, and is screw-engaged with the brake piston, and