The present invention relates to a method for positioning, in a cytoplasm, an antibody having a complete immunoglobulin form, by means of active cell penetration. In addition, the present invention relates to a light chain variable region (VL) that induces the active penetration of a cell membrane of a living cell by an antibody having a complete immunoglobulin form and the positioning of the antibody in the cytoplasm, and an antibody comprising same. Also, the present invention relates to a bioactive molecule fused to the antibody. Also, the present invention relates to a composition for preventing, treating or diagnosing cancer, comprising the antibody or the bioactive molecule fused to same. The present invention also relates to a polynucleotide that codes the light chain variable region and the antibody. The present invention also relates to a method for preparing an antibody that is made to penetrate through to the inside of a cell and positioned in the cytoplasm.