In this study, the verification test and creep test for both a single-rebar nail and a multi-rebar nail are carried out to investigate a tensile strength for both nails. The adhesion effects between a rebar and a cement grout, a mobilized frictional force induced by pull-out load, and load transfer characteristics are examined. The results obtained from the field pull-out tests and from the numerical analysis using $FLAC^{2D}$ which is one of the programs developed based on the finite difference method are analyzed and compared for a single-rebar nail and a multi-rebar nail. The field pull-out test results for a multi-rebar nail relative to a single-rebar nail show that a tensile failure load is relatively large and the pull-out loads are well transferred to the ground in deep depth.