The present invention provides a fusion protein of an antigen-binding protein and a fluorescent protein or a fluorescence-labeled tag protein. The present invention provides a fusion protein of an antigen-binding protein and a fluorescent protein or a fluorescence-labeled tag, wherein the antigen-binding protein is an antigen-binding protein having a helix structure or a β-sheet structure at a terminus, the fluorescent protein or the fluorescence-labeled tag is a fluorescent protein or a fluorescence-labeled tag having a helix structure or a β-sheet structure at a terminus, and the helix at the terminus and the helix at the terminus are linked, or the β-sheet structure at the terminus and the β-sheet structure at the terminus are linked.