To provide a diazonium salt having high solubility to organic solvent and excellent light decomposing property to light source having 350-500 nm wavelength area.

This diazonium salt is characterized by being represented by the following general formula (I) [R1, R2, R3, R4, R5, R6, R7 and R8 are each independently hydrogen atom, a halogen, an alkyl group, an alkoxy group, an alkylthio group or an arylthio group; R9 is hydrogen atom, an alkyl group or an alkoxy group; X- is an anion, with the proviso that at least one group of R1, R2, R3, R4, R5, R6, R7, R8 and R9 is ≥7C group].