To provide a therapy and a diagnosis of cancer or an infection using recognition mechanism of a T-cell receptor. An NK cell function enhancer comprises, an active ingredient, a T-cell receptor chimeric protein being a fusion protein of: a T-cell receptor variable region capable of recognizing a cancer-specific antigen or a T-cell receptor variable region capable of recognizing an antigen specific to a pathogen causative of an infection, and an immunoglobulin Fc region, wherein the T-cell receptor chimeric protein binds to an MHC molecular complex of a cancer cell to down-modulate an MHC class I molecule complex, and the cancer cell is killed or damaged by recognition of an NK cell; and an NK cell function enhancer for imparting to an NK cell a function of recognizing a cancer cell or an infected cell infected with a pathogen causative of an infection, which expresses an MHC class I molecule, and killing or damaging the cancer cell or the infected cell by TDCC (T-cell receptor chimeric protein-dependent cellular cytotoxicity) activity.