A thermoelectric device includes a tubular electrode filled with an electrolyte, a core rod electrode inserted in the tubular electrode and in contact with the electrolyte, and at least one plug configured to separate the tubular electrode from the core rod electrode and to cover a filling opening of the tubular electrode. The plug is located between the tubular electrode and the core rod electrode. When the tubular electrode and the core rod electrode have a temperature difference, thermal energy can be directly converted into electric energy by the redox reaction of the electrolyte, and the tubular electrode and the core rod electrode can generate electromotive force. In particular, the thermoelectric device may use the structural design between the tubular electrode and the core rod electrode to provide a greater contact area with a heat source, and may be directly immersed in a heat source.