A biometric security device for digital key storing is disclosed. The biometric security device includes a biometric information fetching module and a processing module. The processing module has a nonvolatile storage unit and a processing unit. The nonvolatile storage unit includes a secure storage unit and a general storage unit. The biometric security device with a secure electronic key designed for storing secret data utilizes both TrustZone™ technology (or similar technology) and biometric authentication. Thus, it can provide the flexibility for multiple users or applications to use the biometric security device or any equipment the biometric security device mounted in without compromising the safeguard of the data stored therein.