PROBLEM TO BE SOLVED: To provide a control method of a load circuit which enables miniaturization of an electric wire and a semiconductor switch by using a switch circuit that simulates a fuse.SOLUTION: A tolerable temperature of an electric wire is set to be a pseudo tolerable temperature which is lower than an actual value, and a conductor resistance r that is used in a heating temperature expression and a heat radiation temperature expression is changed to a pseudo conductor resistance r* and a heat resistance R is changed to a pseudo heat resistance R*, for calculating a heat generation value and heat radiation value of the electric wire, thus a current electric wire temperature is estimated. When the estimated temperature reaches the pseudo tolerable temperature, an electric switch S1 is shielded, for protecting a load circuit. As a result, both of a semiconductor switch and an electric wire used in the load circuit can be protected from overheating.
