An adjusting mechanism adapted to adjust a position of a projection unit relative to a fixing object is provided. The adjusting mechanism includes a base, a sliding plate, a first screw, and an elastic element. The base is adapted to be fixed to the fixing object. The sliding plate is slidably disposed on the base along a first axis and adapted to be fixed to the projection unit. The first screw is fixed to the sliding plate and screwed to the base, wherein the first screw drives the projection unit to move relatively to the base along the first axis when the first screw is rotated. The elastic element is compressed between the base and the sliding plate along the first axis.