To obtain a diazonium salt important as a heat sensitive recording material and a heat sensitive recording material excellent in optical fixing and hardly having a color of texture.

This diazonium salt is expressed by general formula (1) [wherein R1, R2, R3, R4, R5, R6, R7 and R8 independently express each H, a halogen, an alkyl, an alkoxy, an alkylthio or an arylthio; R9 and R10 independently express each H, an alkyl or an aryl; R2 and R3, R1 and R4, R3 and R6, R4 and R5, R6 and R7, R5 and R8, R7 and R9, R8 and R10 and R9 and R10 may each form a ring by bonding to each other; X- expresses an anion]. This heat sensitive recording material contains the diazonium salt.