It is to provide photodynamic therapy (PDT) and photodynamic diagnosis (PDD) which are suitable for the diagnosis and therapy of a part requiring a certain degree of deep penetration, such as subcutaneous cancer and lymph nodes surrounded by blood vessels and fat. This is solved by performing PDT and PDD targeting cancer by administering a composition comprising a photosensitizing agent such as a tetrapyrrole-based compound (photofrin, protoporphyrin IX, etc.) or ALAs such as 5-aminolevulinic acid (ALA), ALA methyl ester, ALA ethyl ester, ALA propyl ester, ALA butyl ester, ALA pentyl ester, or a hydrochloride, phosphate, or sulfate thereof followed by irradiation with excitation light at a wavelength of 480 to 580 nm.
