[en] A position sensitive single wire proportional counter (PS-SWPC) with supplemental electrodes is studied for developing a focal plane detector of a magnetic spectrograph. These electrodes increase the electric field at the position away from the anode wire in the counter in order to accelerate the drift velocity of electrons generated by the incident radiation. Characteristics of electron drift and detection efficiency for filling gas mixtures (Ar-CH₄ and Ne-CH₄) are investigated. As a result, we obtained sufficient time characteristics for PS-SWPC. (author)