  Using multi-wavelength observations of SoHO/MDI, SOT-Hinode/blue-continuum
(4504 \AA), G-band (4305 \AA), Ca II H (3968 \AA) and TRACE 171 \AA, we present
the observational signature of highly twisted magnetic loop in AR 10960 during
the period 04:43 UT-04:52 UT at 4 June, 2007. SOT-Hinode/blue-continuum (4504
\AA) observations show that penumbral filaments of positive polarity sunspot
have counter-clock wise twist, which may be caused by the clock-wise rotation
of the spot umbrae. The coronal loop, whose one footpoint is anchored in this
sunspot, shows strong right-handed twist in chromospheric SOT-Hinode/Ca II H
(3968 \AA) and coronal TRACE 171 \AA\, images. The length and the radius of the
loop are $L\sim$80 Mm and $a\sim$4.0 Mm respectively. The distance between
neighboring turns of magnetic field lines (i.e. pitch) is estimated as
$\approx$ 10 Mm. The total twist angle, $\Phi\sim$12$\pi$ (estimated for the
homogeneous distribution of the twist along the loop), is much larger than the
Kruskal -Shafranov instability criterion. We detected clear double structure of
the loop top during 04:47-04:51 UT on TRACE 171 \AA \ images, which is
consistent with simulated kink instability in curved coronal loops
(T{\"o}r{\"o}k et al. 2004). We suggest, that the kink instability of this
twisted magnetic loop triggered B5.0 class solar flare, which occurred between
04:40 UT and 04:51 UT in this active region.
