In the framework of WZW-like open superstring field theory (SSFT) including the Ramond (R) sector whose action was constructed by Kunitomo and Okawa, we truncate the string fields in both the Neveu-Schwarz (NS) and R sectors up to the lowest massless level and obtain the ten-dimensional super Yang-Mills (SYM) action with bosonic extra term by explicit calculation of the SSFT action.Furthermore, we compute a contribution from the massive part up to the lowest order and find that the bosonic extra term is canceled and instead a fermionic extra term appears, which can be interpreted as a string correction to the SYM action. This calculation is an extension to the R sector of the earlier work by Berkovits and Schnabl in the NS sector. We also study gauge transformation, equation of motion, and spacetime supersymmetry transformation of the massless component fields induced from those of string fields. * Present address:

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