An electric-wire protection device that protects an electric wire by cutting off power to the wire when its temperature is elevated above a predetermined value is presented. The device includes switching means to control the conduction of power to the wire, current measuring means to measure a current in the wire, environment temperature detecting means to detect a temperature of the environment surrounding the wire, electric-wire temperature calculating means to calculate the temperature of the wire using the value of the current in the wire and the environment temperature, limiting means to stop the conduction of power to the wire when the temperature is greater than or equal to a predetermined value, peripheral component current measuring means to measure the current flowing to a component at the periphery of the environment temperature detecting means, thermal influence acquisition means to obtains an amount of temperature increase caused by the component at the environment temperature detecting means, and environment temperature correcting means to correct the environment temperature based on the amount of temperature increase.