  We report the broad-band spectral properties of the X-ray pulsar Cep X-4 by
using a Suzaku observation in 2014 July. The 0.8-70 keV spectrum was found to
be well described by three continuum models - Negative and Positive power-law
with Exponential cutoff (NPEX), high energy cutoff power-law and CompTT models.
Additional components such as a cyclotron line at $\sim$28 keV and two Gaussian
components for iron lines at 6.4 and 6.9 keV were required in the spectral
fitting. Apart from these, an additional absorption feature at $\sim$45 keV was
clearly detected in residuals obtained from the spectral fitting. This
additional feature at $\sim$45 keV was clearly seen in phase-resolved spectra
of the pulsar. We identified this feature as the first harmonic of the
fundamental cyclotron line at $\sim$28 keV. The ratio between the first
harmonic and fundamental line energies (1.7) was found to be in disagreement
with the conventional factor of 2, indicating that the heights of line forming
regions are different or viewed at larger angles. The phase-resolved
spectroscopy of the fundamental and first harmonic cyclotron lines shows
significant pulse-phase variation of the line parameters. This can be
interpreted as the effect of viewing angle or the role of complicated magnetic
field of the pulsar.
