In a blockchain system, a blockchain transaction is protected against forgery by adding a digital signature. By digital signature verification, we can confirm that a creator of a transaction has a correct private key. However, in some critical fields, we need to prove that a creator of a transaction is a proper user. In such a case, the conventional digital signature verification cannot achieve sufficient security. Furthermore, a system that combines blockchain and IoT has been proposed. However, since an IoT device in this system automatically generates a blockchain transaction, reliable creator verification is challenging issue. To achieve reliable creator verification in the IoT blockchain system, we propose a new signature scheme for blockchain. Our contributions are as follows: (1) We propose a new secure and practical signature scheme. (2) We implement our signature scheme for an IoT blockchain system and evaluate the security and the practicality of our scheme. In our scheme, by using user’s biometric information as a private key, we prove that a creator of a transaction has a correct biometric information in the transaction verification. Since biometric information such as fingerprint, face, finger vein and so on is unique, this means that a creator of a transaction is a proper user. Moreover, the proposed signature scheme generates a short-term private key and utilizes it for creating transactions. By using this scheme, IoT device can automatically generate a new transaction. Finally, we evaluate security and practicality of the proposed scheme.