An attachable wireless charging device includes a carrier board, a receiving coil, a circuit board, and at least two conductive wires. The carrier board has a back surface on which an adhesive layer is coated. The receiving coil is formed in the carrier board. The circuit board is mounted to one side of the carrier board and includes a power receiving circuit, which includes a receiving control circuit, a resonance control circuit, a regulation circuit, a control circuit, a polarity selection circuit, and a circuit output section, which are electrically and sequentially connected. Electrical connection is established between the receiving control circuit and the receiving coil. The at least two conductive wires are arranged at one side of the circuit board and are electrically connectable with the circuit output section of the circuit board. As such, an attachable wireless charging device featuring automatic determination of polarity connection is provided.