A sliding door safety device for heavy construction equipment is provided, which includes an outer side wall having a doorway formed thereon, an upper rail and a lower rail formed on an upper part and a lower part of the outer side wall, respectively, a sliding door sliding to move to a front or rear side of a cab by an upper roller and a lower roller engaged with the upper rail and the lower rail, respectively, to open or close the doorway, and first and second door position sensing switches mounted on one side of the outer side wall to sense a door position when the door is in its open position where the door is fully opened or in its closed position where the door is fully closed.