The invention discloses an automatic letter box device, comprising a main seat body; footings are fixedly arranged around the end face of the bottom of the main seat body; the bottom ends of the footings are fixedly provided with non-slip mats; a transfer cavity is arranged in the end face of the top of the main seat body; a transfer rack is installed at the upper side of the interior of the transfer cavity in a running fit way; the transfer rack is internally provided with rotary arms, which are symmetrical at left and right, in a running fit way; the top end of each rotary arm is provided with a winding mechanism, and the bottom end face of each rotary arm is internally provided with a spline groove; an adapter spindle is fixedly arranged just in the center of the bottom end of the transfer rack; the adapter spindle is connected with the bottom wall in the transfer cavity in a running fit way; a first meshing gear is fixedly arranged along the circumferential direction of the outer surface of the adapter spindle; a first motor is fixedly arranged in the main seat body at the lower side of the transfer cavity; first sliding grooves are respectively formed at the left side and right side of the first motor in a symmetrical way; each first sliding groove is internally provided with a first sliding plate in a sliding fit way.