Provided are a resistive memory device including a plurality of memory cells, and a method of operating the resistive memory device. The resistive memory device includes a sensing circuit connected to a first signal line, to which a memory cell is connected, the sensing circuit sensing data stored in the memory cell based on a first reference current; and a reference time generator for generating a reference time signal that determines a time point when a result of the sensing is to be output, based on the first reference current.