  The dependence of the $K^+ \to \pi^0 l^+ \nu_l \gamma$ decay width on the
$T$-odd kinematical variable, $ \xi = {\vec q \cdot [\vec p_l \times \vec
p_\pi]} / {M^3}$, is studied at the tree and one-loop levels of Standard Model.
It is shown that at the tree level this decay width is the even function of
$\xi$, while the odd contribution arises due to the electromagnetic final state
interaction. This contribution is determined by imaginary parts of one-loop
diagrams. The calculations performed show that the $\xi$-odd contribution to
the $K^+ \to \pi^0 e^+ \nu_e \gamma$ and $K^+ \to \pi^0 \mu^+ \nu_\mu \gamma$
decay widths is four orders of magnitude smaller than even contribution coming
from the tree level of SM.
