[en] The subharmonic prebuncher system of the Osaka University Single Bunch Electron Linear Accelerator has been improved in order to increase a single bunch charge form 14 nC to 60 nC. Such most appropriate bunching condition for a large current beam injection into acceptance angle of a prebuncher was calculated by a one-dimensional disk model. The previous 6 th subharmonic prebuncher (SHPB) was replaced with two 12 th SHPBs and 6 th SHPB that are newly constructed. In January, 1984 the single bunch beam succeeded in an acceleration up to 67 nC over a goal. The bunch compressor was installed in the transport system to compress width of the large current single bunch and bunch width was shortened from 20 ps to 9 ps. In order to get the charge of 100 nC, an improvement of the prebuncher rf system, also development of an avalanche pulser and a new type electron gun are planned. (author)