A protection device includes a connecting portion, power supply means, temperature detection means, temperature determination means, and prohibition means. The connecting portion is configured to be coupled with an external device for sending and receiving information with the external device. The power supply means supplies electric power to the external device through the connecting portion. The temperature detection means detects temperature in a vehicle compartment, and the temperature determination means determines whether the detected temperature is within a predetermined temperature limit. The prohibition means stops the power to the external device when the temperature determination means determines that the detected temperature is out of the predetermined temperature limit.