Medical records are very important records and should not be modified after creation. The current medical records are liable to improper modification. With the development of information technology, electronic medical records (EMR) are used widely. For the EMR, cryptographic primitives may be used to develop techniques to prevent medical record modofication. In this research, a technique to prevent improper medical record prevention is proposed. It uses crytographic primitives such as linked hash, digital signature, and electronic notarization. A prototype system is also developed for performance analysis. The proposed method makes the medical record modification impossible with a small amount of additional cost.