To provide a wire protective device for vehicle which can protect a wire by calculating the temperature of the wire at a low cost with a high speed.

In a wire protective device 100 for vehicle, an additional temperature-rise value ΔT1(n) is calculated, in advance, by using the drain-source voltage Vds(n-1) and the case temperature Tc(n-1) as parameters, in order to reduce the load of arithmetic processing as much as possible, and it is stored in a memory 140 as a heat generation data array. The residual temperature-rise value ΔT2(n) is also calculated, in advance, by using the temperature-rise value ΔTw(n-1) of previous period as a parameter, and the result is stored in the memory 140 as a heat radiation data array. A wire temperature operation unit 130 estimates the temperature Tw of a wire 30 by reading the additional temperature-rise value ΔT1(n) and the residual temperature-rise value ΔT2(n) from the heat generation data array and the heat radiation data array.