An apparatus and operating method of a nonvolatile memory device having three-level nonvolatile memory cells is used to store more than one bit of data in a nonvolatile memory cell. In addition, the data can be selectively written through a write-verify operation, thereby improving write operation reliability. The operating method includes providing a memory cell array having first through third nonvolatile memory cells where each memory cell is capable of storing one among first data through third data corresponding to first through third resistance levels, respectively. Each of the resistance levels is different from one another. First and the third data are written to the first and third nonvolatile memory cells, respectively, during a first interval of a write operation. Second data is written to the second nonvolatile memory cell during a second interval of the write operation.