An atmospheric pressure plasma torch is generated with a hollowneedle-to-plate dielectric barrier discharge and the electron densities in the inside and at the surface of the plasma torch are measured by optical emission spectroscopy (OES). A plasma torch with 1cm long is generated in atmospheric ambient when argon gas is introduced through the hollwneedle. The Stark broadenings of Hα and ArⅠ(696.54 nm) lines, which are decomposed from the experimental profiles by using deconvolution method, are used to estimate the corresponding electron densities. The electron densities are 1.0×1015 cm－3 and 3.78×1015 cm－3 corresponding to the Stark broadening of Hα and ArⅠ(696.54 nm) lines, respectively. The electron density calculated from the Stark broadening of Hα is the same as that at the surface of the plasma because Hα line originates from the dissociation and the excitation of H\-2O at the plasma torch surface where argon can meet with atmosphere. While the electron density calculated from the Stark broadening of ArⅠ(696.54 nm)line is the same as that in the insid of plasma.