  We report the results of an analysis of data obtained with the INTEGRAL,
Swift and RXTE observatories during the 2010 April and September outbursts of
the X-ray pulsar RX J0440.9+4431. The temporal and spectral properties of the
pulsar in a wide energy band (0.6-120 keV) were studied for the first time. We
discovered a ~32 keV cyclotron resonant scattering feature in the source
spectrum, that allowed us to estimate the magnetic field strength of the
neutron star as B~3.2 x 10^12 G. The estimate of the magnetic field strength
was confirmed by a comprehensive analysis of the noise power spectrum of the
source. Based on the recurrence time between Type I outbursts the orbital
period of the binary system can be estimated as ~155 days. We have shown that
the pulse profile has a sinusoidal-like single-peaked shape and has practically
no dependence on the source luminosity or energy band.
