Disclosed is a security key device for cloud services. The security key device includes an interface unit that provides an interface with the user terminal, a storage unit that stores an encrypted user file, and an encryption / decryption conversion support controller that encrypts, when a file to be uploaded to a cloud server is received from the user terminal, the received file and stores the encrypted file in the storage unit to transmit the encrypted file to the user terminal, and stores, when an encrypted file downloaded from the cloud server is received from the user terminal, the received encrypted file in the storage unit and decrypts the encrypted file to transmit the decrypted file to the user terminal. Even when a cloud server is hacked, individual and company's important data cannot be opened, encryption / decryption is processed in a hardware encryption accelerator, and therefore it is possible to prevent leakage of an encryption key even when a personal PC is hacked, thereby significantly improving security compared to the related art.