[Problem] To provide an anti-human MUC1 antibody Fab fragment, which is expected to be useful for the diagnosis and/or treatment of cancer, particularly the diagnosis and/or treatment of breast cancer or bladder cancer, and a diagnosis means and/or a therapeutic means using a complex containing the Fab fragment. [Solution] An anti-human MUC1 antibody Fab fragment which contains a heavy chain fragment containing a heavy-chain variable region comprising the amino acid sequence represented by SEQ ID NO: 8 or 10, and a light chain containing a light-chain variable region comprising the amino acid sequence represented by SEQ ID NO: 12； and a complex containing the Fab fragment.
