Layout of a high-speed signal wiring on a power supply plane is checked and
specified at an optimum position capable of minimizing a spurious
electromagnetic radiation so as not to affect other wiring layers. When a
high speed signal line which is an object to be checked exists on a power
supply plane, a perpendicular distance between the high speed signal line
and the plane which is nearest to the signal line is determined, and
compared with a minimum required distance computed therefor in advance on
the basis of its circuit specification of the high speed signal line. If
the perpendicular distance determined does not exceed the minimum required
distance computed, an appropriate message corresponding to the name of the
high speed signal line is displayed.
