Disclosed is an anti-CD4 antibody which can bind to CD4 with high affinity and exhibits a high effector activity such as a high antibody-dependent cellular cytotoxicity (ADCC activity) or a high complement-dependent cellular cytotoxicity (CDC activity) in diseases associated with CD4-expressing cells. Specifically disclosed are: a monoclonal antibody which can recognize an extracellular region of CD4 specifically to bind to the extracellular region with high affinity, and can exhibit a high ADCC activity or a high CDC activity, or a fragment of the antibody; a hybridoma which can produce the antibody; DNA which encodes the antibody; a vector which carries the DNA; a transformant which is produced by introducing the vector; a method for producing an antibody or a fragment thereof utilizing the hybridoma or the transformant; a therapeutic agent comprising the antibody or a fragment thereof; and a diagnostic agent comprising the antibody or a fragment thereof.
