  We present the first spectropolarimetric observations of a candidate of
super-Chandrasekhar mass Type Ia supernova (SN): SN 2009dc. The observations
were performed at 5.6 and 89.5 days after the B-band maximum. The data taken at
the later epoch are used to determine the interstellar polarization. Continuum
polarization is found to be small (<0.3 %), indicating that the explosion is
nearly spherically symmetric. This fact suggests that a very aspherical
explosion is not a likely scenario for SN 2009dc. Polarization at the Si II and
Ca II lines clearly shows a loop in the Q-U plane, indicating a
non-axisymmetric, clumpy distribution of intermediate-mass elements. The degree
of line polarization at the Si and Ca line is moderate (0.5% +- 0.1% and 0.7%
+- 0.1%, respectively), but it is higher than expected from the trend of other
Type Ia SNe. This may suggest that there are thick enough, clumpy Si-rich
layers above the thick 56Ni-rich layers (>~ 1.2 Msun). The observed
spectropolarimetric properties, combined with the photometric and spectroscopic
properties, suggest that the progenitor of SN 2009dc has a super-Chandrasekhar
mass, and that the explosion geometry is globally spherically symmetric, with
clumpy distribution of intermediate-mass elements.

Cosmology and Nongalactic Astrophysics;Solar and Stellar Astrophysics