There is provided a fluid pressure drive unit that can fulfill a position holding function stably even when an external force acts during the time when the position is held, the unit being used, for example, for the right and left angle adjustment of a snow plow blade. There is provided a first excessive load relief valve 6 for letting a working fluid escape from a bottom-side pipe line 10a, whichconnects the bottom-side port of a single-rod double acting cylinder 2 to the bottom side of an operate check valve 4, to a rod-side pipe line 10b, which connects the rod-side port of the single-roddouble acting cylinder 2 to the rod side of the operate check valve 4, and there is provided a second excessive load relief valve 7 for letting the working fluid escape from the rod-side pipe line 10bto a tank 3. Also, there is provided a negative pressure preventing check valve 8 for allowing the working fluid to flow into the bottom-side pipeline 10a from the tank 3.