A signal transmission apparatus comprises a base and a shell, wherein a top portion of the base has a signal transmission device. The shell is covered above the base. A cavity is formed inside the shell. The cavity is in communication with an opening of a bottom portion of the shell. And the shell comprises a ceramic shell body and an inner covering layer. The inner covering layer is fully attached to an inner surface of the ceramic shell body. Therefore, the signals of the signal transmission device can pass through the shell so that the signal transmission device can receive or transmit signals. And through the strong adhesion of the inner covering layer, the ceramic shell body can be kept intact without being broken into a lot of debris when the ceramic shell body is impacted by external force or suddenly dropped.