An
overcurrent detection device is provided in which the accuracy of the
overcurrent detection is high, even if there is a location where the temperature is unknown due to a large instantaneous current. An
overcurrent detection device 11 comprises: an instantaneous current
estimation unit 101, which estimates an instantaneous current I at location X, where the temperature is unknown, based on an instantaneous
voltage V measured in a conductor 111 and an estimated resistance R at location X; an overcurrent determination unit 102, which determines whether an overcurrent is present based on the estimated instantaneous current I; and a
power consumption calculation unit 103, which calculates a
power consumption P based on the instantaneous
voltage V and the estimated instantaneous current I.a temperature
estimation unit 104 that estimates and updates a temperature T at location X, where the temperature is unknown, based on a thermal
equivalent circuit Tmodel that takes into account at least a
thermal resistance Rth and a thermal
capacitance Cth of the conductor 111, the
absorbed power P, and a known temperature Ta and Tt at at least one location in the conductor 111; and a resistance
estimation unit 105 that updates the estimated resistance R at location X, where the temperature is unknown, based on the updated temperature T.