Context :

Aims:4U 2206+54 is a wind-fed high mass X-ray binary with a main-sequence donor star .
The nature of its compact object was recently identified as a slow-pulsation magnetized neutron star .

Methods : INTEGRAL/IBIS observations have a long-term hard X-ray monitoring of 4U 2206+54 and detected a hard X-ray outburst around 15 December 2005 combined with the RXTE/ASM data .

Results : The hard X-ray outburst had a double-flare feature with a duration of \sim 2 days .
The first flare showed a fast rise and long time decaying light curve about 15 hours with a peak luminosity of \sim 4 \times 10 ^ { 36 } erg s ^ { -1 } from 1.5 – 12 keV and a hard spectrum ( only significantly seen above 5 keV ) .
The second one had the mean hard X-ray luminosity of 1.3 \times 10 ^ { 36 } erg s ^ { -1 } from 20 – 150 keV with a modulation period at \sim 5550 s which is the pulse period of the neutron star in 4U 2206+54 ; its hard X-ray spectrum from 20 – 300 keV can be fitted with a broken power-law model with the photon indexes \Gamma _ { 1 } \sim 2.3 , \Gamma _ { 2 } \sim 3.3 , and the break energy is E _ { b } \sim 31 keV or a bremsstrahlung model of kT \sim 23 keV .

Conclusions : We suggest that the hard X-ray flare could be induced by suddenly enhanced accretion dense materials from stellar winds hitting the polar cap region of the neutron star .
This hard X-ray outburst may be a link to supergiant fast X-ray transients though 4U 2206+54 has a different type of companion .