Multi-colour staining with fluorescent dyes is actively used for observing the distribution of biological materials (such as proteins, lipids, nucleic acids, and ions) in the field of tissue and cell research. The detection technology for fluorescence observation has advanced to a level at which a single fluorescent dye molecule can be detected under the best of circumstances. Fluorescence lifetime imaging microscopy (FLIM)is a new fluorescence microscopy technology. In addition to multi-colour staining, fluorescence lifetime imaging can be utilised to visualise the factors that affect the fluorescence lifetime properties of the dye molecule, that is, the state of the environment around the molecule.