PURPOSE: To enable free rotation of an output shaft without separating the output shaft from a hydraulic motor.

CONSTITUTION: In a hydraulic driving mechanism provided with a hydraulic motor 1 rotated by receiving supply of pressure oil, a reduction gear 20 connected to an output shaft 2 of the hydraulic motor 1 and a hydraulic brake 7 for regulating rotation of the output shaft 2, there are provided a movable piston member 15 for having hydraulic pressure work on the piston 9 which releases the hydraulic brake 7 and an unload valve 4 for making a supply port and discharge port 1A and 1B of working oil of the hydraulic motor 1 communicate with each other.