A relay temperature measuring device is provided. The device includes a sensor that measures an output of a battery and generates output measurement information and one or more relays that are disposed on a conductive line between the battery and a load. Additionally, a controller compares a relay temperature calculated using both-end measurement power information generated by measuring both ends of a conductor in a vehicle and the output measurement information with a preset temperature reference value, and connects or disconnects the relays based on a comparison result.