  I propose a method to detect planets around compact binaries that are strong
sources of gravitational radiation. This approach is to measure
gravitational-wave phase modulations induced by the planets, and its prospect
is studied with a Fisher matrix analysis. I find that, using the Laser
Interferometer Space Antenna (LISA), planets can be searched for around ~3000
Galactic double white dwarfs with detection limit ~4 M_J (M_J~ 2x10^{30}g: the
Jupiter mass). With its follow-on missions, planets with mass ~1 M_J might be
detected around double neutron stars even at cosmological distances z~1. In
this manner, gravitational wave observation has potential to make interesting
contributions to extra-solar planetary science.
