  It is known that geometrical optics no longer applies to the gravitational
lensing if the wavelength of a propagating wave becomes comparable to or larger
than the Schwarzshild radius of a lensing object. We investigate the
propagation of gravitational waves in wave optics, particularly focusing on the
difference between their arrival time and the arrival time of light. We argue
that, contrary to the observation in the previous work, gravitational waves
never arrive at an observer earlier than light when both gravitational waves
and light are emitted from a same source simultaneously.
