A post driver unit includes a frame having a quick connect attachment to a front end loader vehicle in place of a bucket or for connecting the unit to a tractor using a three point hitch. The frame supports a vertical mast for rotation on a vertical axis by fluid actuated cylinder, and the mast supports an elongated boom for pivotal movement on a horizontal axis. A fluid actuated impact driver depends directly from an outer end portion of the boom by a universally supported connector member to provide the impact driver with a vertical axis, and the boom is pivoted by a fluid actuated cylinder system which provides for rapidly raising the boom and the impact driver and lowering the boom and impact driver at a controlled slower rate. The connector member may have different lengths according to the length of the post to be driven.