The present invention provides a method of detecting a target nucleic acid
which includes a step of examining whether a washing step has been
normally conducted. In an aspect of the invention, a monitoring nucleic
acid probe to monitor the washing level is used. The probe shows a change
in signal intensity by washing at a washing temperature changed in the
optimum temperature range for washing the target nucleic acid and in a
temperature range in the vicinity of the optimum temperature range for
washing.