  We report a measurement of the direct CP violation asymmetry parameter $A_g$
in charged kaon decays $K^\pm\to\pi^\pm\pi^+\pi^-$ by the NA48/2 experiment at
the CERN SPS. The experiment has been designed not to be limited by systematics
in the asymmetry measurement. Using $1.67\times 10^9$ such decays collected
during the 2003 run, the charge asymmetry in the Dalitz plot linear slope
parameter $g$ has been measured to be $A_g=(1.7\pm2.9)\times 10^{-4}$. The
precision of the result is limited by the statistics used.
