The wide-band energy spectrum of NGC 6240 over the range 0.5-200 keV is inv
estigated using the RXTE and ASCA data. The RXTE data provide the spectrum
beyond the ASCA range (0.5-10 keV) with significant detection of signals up
to 30 keV and upper limits above 20 keV. The spectrum above 10 keV is foun
d to be very flat. A strong iron K emission line discovered in the previous
ASCA observation is also confirmed with the RXTE Proportional Counter Arra
y (PCA), These results provide further evidence for the dominance of a refl
ection component, i.e, emission from cool material illuminated by an active
galactic nucleus (AGN). By fitting the spectra obtained with RXTE and ASCA
simultaneously, we satisfactorily modelled the AGN spectrum with a Compton
reflection component and probably a transmitted AGN component penetrating
through a thick absorber. The X-ray luminosity of the AGN is estimated to b
e in the range 4 x 10(43) to 6 x 10(44) erg s(-1) in the range 2-10 keV, wh
ich categorizes NGC 6240 among the most luminous Seyfert nuclei. The ratio
of the 2-10 keV X-ray luminosity to the infrared luminosity, L-x(2-10 keV)/
L-IR, is 0.01-0.1, which implies a quite substantial, if not dominant, cont
ribution of AGN to the infrared luminosity.