  It is known that the unknotting number $u(L)$ of a link $L$ is less than or
equal to half the crossing number $c(L)$ of $L$. We show that there are a
planar graph $G$ and its spatial embedding $f$ such that the unknotting number
$u(f)$ of $f$ is greater than half the crossing number $c(f)$ of $f$. We study
relations between unknotting number and crossing number of spatial embedding of
a planar graph in general.
