In a normal data reading, one of word lines and one of first and second dummy
word lines are selected and data is read out through the access to selected regular
memory cell and a reference cell. In a test mode, each of word lines are turned
to a non-select state and both of first and second dummy word lines are selected
and by setting one of first and second reference voltages to a level different
from a level during the normal data reading, data is read out through the access
to the reference cells.
