Disclosed is a nonvolatile memory device, which includes a memory cell array including cell strings, a row decoder connected with a ground selection transistor of each of the cell strings through a ground selection line, connected with memory cells of each of the cell strings through word lines, and connected with a string selection transistor of each of the cell strings through a string selection line, and a page buffer connected with the cell strings through bit lines. In a first period of a check operation, the page buffer applies a first bias voltage to the bit lines, and the row decoder applies a turn-off voltage to the ground selection line, a turn-on voltage to the string selection line, and a first check voltage to the word lines. In a second period of the check operation, the page buffer senses first changes of voltages of the bit lines.