  We present observations with the INTEGRAL/IBIS telescope of the wind nebula
powered by the young pulsar B1509-58 and we discuss the spatial and spectral
properties of the unpulsed emission in the 20-200 keV energy band. The source
extension and orientation along the northwest-southeast axis corresponds to the
jet emission seen at keV and TeV energies. The hard X-ray spectrum is
consistent with the earlier Beppo-SAX measurements. It follows a power law with
a photon index alpha = -2.12 pm 0.05 up to 160 keV. A possible break at this
energy is found at the 2.9 sigma confidence level. The 0.1-100 keV data are
consistent with synchrotron aging of pairs in the jet and yield a magnetic
field strength of 22-33 muG for a bulk velocity of 0.3-0.5c. The synchrotron
cut-off energy thus corresponds to a maximum electron energy of 400-730 TeV.
