New psoralen compound

A compound represented by the following formula (I) or a salt thereof:

• wherein
• R1 is a hydrogen atom, an aliphatic group having 1 to 3 carbon atoms, or —O—R7 [where R7 is a hydrogen atom or an aliphatic group having 1 to 3 carbon atoms], or is represented by the following formula (II-1), (II-2), or (II-3):
• [in the formulae (II-1), (II-2), and (II-3), R8 is a hydrogen atom, an aliphatic group having 1 to 3 carbon atoms, or —N(R9)2 or —O—R9 [where R9 is a hydrogen atom or an aliphatic group having 1 to 3 carbon atoms]],
• R2 is a hydrogen atom, an aliphatic group having 1 to 3 carbon atoms, or —O—R10 [where R10 is a hydrogen atom or an aliphatic group having 1 to 3 carbon atoms],
• R3 and R4 are each independently a hydrogen atom, an aliphatic group having 1 to 3 carbon atoms, —O—R11 [where R11 is a hydrogen atom or an aliphatic group having 1 to 3 carbon atoms], or a phenyl group or naphthyl group in which each hydrogen atom may be substituted with an aliphatic group having 1 to 3 carbon atoms, or alternatively,
• R3 and R4 together form a benzene ring or naphthyl ring in which each hydrogen atom may be substituted with an aliphatic group having 1 to 3 carbon atoms,
• R5 is represented by the following Formula (III-1) or (III-2):
• [in the formulae (III-1) and (III-2),
• m is an integer of 0 to 4,
• n is an integer of 1 to 5, and
• R13 and R14 are each independently a hydrogen atom, an aliphatic group having 1 to 3 carbon atoms, or a polar group], and
• R6 is a hydrogen atom, an aliphatic group having 1 to 3 carbon atoms, or —O—R12 [where R12 is a hydrogen atom or an aliphatic group having 1 to 3 carbon atoms].