PHOTOFIXING-TYPE THERMAL RECORDING MEDIUM

PROBLEM TO BE SOLVED: To provide a photofixing-type thermal recording medium which is substantially free from the deterioration of a color developing activity of a second color when data is printed in the second color after printing data in a first color and leaving it alone indoors for a long time. SOLUTION: This photofixing-type thermal recording medium is made up of a recording layer, firmed on a support, which contains a first diazonium salt which produces a coloring matter contributing to the printing of data in a first color through a chemical reaction with a coupler and loses an activity by irradiation with a first light, a second diazonium salt which produces a coloring matter contributing to the printing of data in, at least, a second color through a chemical reaction with the coupler and loses an activity by irradiation with a second light with a different wavelength from the first light, at least, one type of coupler and a basic chemical compound. The first diazonium salt is 4-(4'-methylphenylthio)-2,5-diethoxybenzenediazonium hexafluoro phosphate. The second diazonium salt is 4-diazo-4'-n-butyldiphenylether hexafluorophosphate.