To surely protect a wiring path from heating, by keeping changes of a line current as a history in the duration of an excess current to early actuate a cutoff mechanism.

In an electronic molded-case circuit breaker, a CPU determines the excess current based on the detected value of the line current, accumulates the duration of the excess current, and opens a main contact by actuating a trip coil when the accumulated value reaches an upper limit value. When the line current increases, the duration is accumulated by an addition coefficient, and when the line current decreases, the accumulated value during the increase is accumulated by two subtraction coefficients. In an initial section of the decrease, the first substraction coefficient having a large value is applied, and after that, the second substraction coefficient having a small value is used. The addition coefficient is set at a value smaller than the first substraction coefficient and larger than the second subtraction coefficient, and the accumulated value of the duration is made approximate to the temperature change in an electric wire.