An orientation adjusting device includes a base unit, a bracket unit, and an angle-adjusting mechanism. The bracket unit is coupled pivotally to the base unit. The angle-adjusting mechanism includes first and second rotatable units and first and second pivot joints. The first pivot joint interconnects the bracket unit and the first rotatable unit so as to permit rotation of the first rotatable unit relative to the bracket unit about a first horizontal axis. The second pivot joint interconnects the base unit and the second rotatable unit so as to permit rotation of the second rotatable unit relative to the base unit about a second horizontal axis parallel to the first horizontal axis. The telescopic unit interconnects the first and second rotatable units, and is operable so as to vary the distance between the first and second horizontal axes.