A compound that comprises Met-Leu-Phe or Nle-Leu-Phe serving as the leukocyte-binding site of a formyl peptide receptor (FPR), a binding part comprising Ser or Thr that increases the binding ratio to monocytes and lymphocytes in all leukocytes, a group that can be labeled with a radioactive metal or a paramagnetic metal, and spacers binding the three moieties together shows binding properties specific to all leukocytes, i.e., neutrophils, monocytes and lymphocytes both in vivo and in vitro. Owing to this characteristic, this compound is highly useful in SPECT image diagnosis, PET image diagnosis, MRI image diagnosis and the like, for imaging sites of inflammation.