A semiconductor memory device comprises a array of memory cells arranged
in a matrix, each memory cell connected to one end of a variable resistor
element where the electric resistance is shifted from the first state to
the second state by applying the first writing voltage and from the
second state to the first state by applying the second writing voltage,
and the source or drain of the selecting transistor. The second writing
time for the second writing action of shifting the electric resistance of
the variable resistor element from the second state to the first state is
longer than the first writing time of shifting the same reversely. The
second number of the memory cells subjected to the second writing action
at once is greater than the first memory cell number subjected to the
first writing action at once, and at least the second number is two or
more.