When we quantize open string field theory, the structure called A∞ plays a crucial role. However, the Berkovits formulation of open superstring field theory, which is one of the most successful formulations of superstring field theory, is based on the large Hilbert space of the superconformal ghost sector, and we have not been able to see the A∞ structure in this formulation. Recently, on the other hand, Erler, Konopka and Sachs succeeded in constructing an action with the A∞ structure by formulating open superstring field theory based on the small Hilbert space. In this talk, we show that this theory with the A∞ structure is related to the Berkovits formulation by field redefinition and partial gauge fixing. This talk is based on an upcoming paper with Erler and Takezaki.