With a wire protection method in accordance with the present invention, the method being used for supplying electric power from a power source to a load, an applied-current to the load is detected every predetermined time, A wire rise temperature is calculated using the detected applied-current I(n) and by a relational expression concerning heat radiation and heat generation of the wire. The calculated rise in temperature is added to a reference temperature so that a wire temperature is estimated. When the estimated wire temperature is lower than a predetermined upper limit temperature, the calculation of the rise in temperature is repeated. When the estimated wire temperature has become equal to or higher than the predetermined upper limit temperature, the electric power supply from the power source to the load is stopped so that the wire is protected.