A connector has a case, a circuit board, and a thermal diffusing unit. The case has an inner surface. The circuit board is mounted in the case and has a heating source. The thermal diffusing unit abuts the inner surface of the case and the heating source of the circuit board. An area of the thermal diffusing unit abutting the inner surface is bigger than an area of the thermal diffusing unit abutting the heating source. A heat transfer coefficient of the thermal diffusing unit is bigger than a heat transfer coefficient of the case. With the structure above, the thermal diffusing unit is allowed to transmit heat from a small area to a big area, thereby improving the heat dissipation efficiency of the connector.