Abstract: A phthalocyanine dye for use in photoimmunotherapy, and a method for producing it, and a conjugate of the phthalocyanine dye and an antibody or a peptide are provided, including—a compound represented by formula (1) or a salt thereof: wherein X represents a substituent having a hydrophilic group at the terminus thereof; L3, L4, L5, and L6 each independently represent a divalent linking group; Y represents a group capable of binding to an antibody or a peptide; R3 represents a substituent, such as an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a halogen atom, —SR11, —SOR12, an aryl group containing 6 to 10 carbon atoms, —N(R13)(R14), or —NO2, wherein when a plurality of R3s are present, the plurality of R3s may be identical to or different from one another; and s represents an integer of 0 to 4.