  The $K_L\to\pi^{\pm}\pi^0e^{\mp}\nu_e(\bar\nu_e)$ decay was investigated with
the NA48 detector at CERN SPS using a beam of long-lived neutral kaons. The
branching ratio $Br(K_L\to\pi^{\pm}\pi^0e^{\mp}\nu_e(\bar\nu_e))=(5.21\pm
0.07_{stat}\pm 0.09_{syst})\times 10^{-5}$ was fixed from a sample of 5464
events with 62 background events. The form factors $\bar{f}_s$, $\bar{f}_p$,
$\lambda_g$ and $\bar{h}$ were found to be in agreement with previous
measurements but with higher accuracy. The coupling parameter of the chiral
Lagrangian $L_3=(-4.1\pm 0.2)\times 10^{-3}$ was evaluated from the data.
