An electric-wire protection device includes a voltage adjustment unit that adjusts the voltage to a load, and a controller that includes a temperature calculation unit that calculates temperature information on an electric wire from a value of current, and makes the voltage adjustment unit into a shut-off state based on the temperature information. The temperature information is calculated from an amount of temperature changes based on the current value and a predetermined initial value. The controller shifts into a sleep state when a sleep condition is satisfied that includes a condition that the temperature information is lower than the initial value. The initial value when the controller returns from the sleep state is based on a convergence value of temperature in conducting energization on the electric wire at a maximum value of steady-state current.