We perform ab initio QED calculation of the (1s)2(2s)22p3/2-(1s)2(2s)22p1/2 transition energy in the five-electron ion of argon. The calculation is carried out by perturbation theory starting with an effective screening potential approximation. Four different types of the screening potentials are considered. The rigorous QED calculations of the two lowest-order QED and electron-correlation effects are combined with approximate evaluations of the third- and higher-order electron-correlation contributions. The theoretical value for the wavelength obtained amounts to 441.261(70) (nm, air) and perfectly agrees with the experimental one, 441.2559(1) (nm, air).