To provide an automatic locking water cup holder which is stable, has a good appearance, prevents a water cup from dropping due to vibration, and is easy to use. [Solution] The automatically locking water cup holder includes a water cup main holder 1, an attachment adapter plate 2, a spring 3, fixed arms 5, 6 and a movable plate 4, the attachment adapter plate is attached to the water cup main holder, the water cup main holder is rotatably connected to the fixed arm via the spring, the tip of the fixed arm is rotatably connected to the movable plate, and the water cup main holder and the movable plate are arranged parallel to each other. The water cup can be fixed to the water cup main holder by fitting the spring, fixed arm and movable plate together.