PROBLEM TO BE SOLVED: To provide a waterproof indicator, that can be used under the existence of water without the occurrence of blur, transcription, and outflow due to the influence of water as in a conventional indicator in AC sterilization, EOG sterilization, retort processing, or boil processing of medical treatment, medicine manufacturing, foot, etc., and also that is economical by suppressing a raw material cost and an employment cost in a simple production process.SOLUTION: A waterproof indicator 1 is constituted by allowing an indicator ink layer 3 formed on at least a part of a front surface of a base material 2 is not covered by a water impermeable film but is exposed or covered by a water permeable resin layer. The indicator ink layer 3 to be discolored at a predetermined temperature and/or in reaction to high-pressure steam or ethylene oxide gas contains monoazo dye to be expressed by a chemical formula (1): A-N=N-B... (1). Compounds in the formula are allowed to be water non-diffusive by hydrophobic groups.
