  The metal-insulator transition (MIT) in vanadium dioxide VO$_2$ due to V-V
dimerization has been extensively discussed for decades. While it is widely
acknowledged that electron correlations, Peierls instabilities, and molecular
orbital formations are crucial for understanding the MIT of VO$_2$, the primary
origin of the MIT remains controversial. In this study, we delve into the
crystal structure and orbital state of VO$_2$ through synchrotron x-ray
diffraction experiments. The molecular orbital formation corresponding to the
V-V dimerization is directly observed in the low-temperature insulating
monoclinic phase, called the M1 phase, as indicated by the valence electron
density distribution. Moreover, diffuse scattering observed in the
high-temperature metal phase of rutile structure suggests the presence of
short-range correlation of V displacements, which is not directly attributed to
the structural fluctuation of the M1 phase. The short-range order in the rutile
phase will be the key to understanding the MIT in this system.
