An insulation resistance measuring device including a positive electrode test resistor connected to a positive electrode node of a battery assembly, a negative electrode test resistor connected to a negative electrode node of the battery assembly, a first switch connecting the positive electrode node of the battery assembly to the positive electrode test resistor, a second switch connecting the negative electrode node of the battery assembly to the negative electrode test resistor, a voltage measurement unit that measures a first voltage applied to the positive electrode test resistor and a second voltage applied to the negative electrode test resistor, and a voltage estimation unit that estimates a final convergence value of the first and second voltages.