The present invention provides a combustion device, which includes a fuel tank assembly and a candle wick. The fuel tank assembly includes a first tank, a second tank, a connection tube, and a switch. The capacity of the second tank is less than the capacity of the first tank. An end of the connection tube is connected to the first tank, and another end of the connection tube is connected to the second tank. The connection tube communicates with internal spaces of the first and second tanks. The switch is disposed between the first and second tanks so as to selectively open or close a channel interconnected between the first and second tanks. The candle wick is mounted in the second tank. Therefore, the combustion device is easy to use by the above structure.