The invention relates to a locking device, in particular to the locking device for calculation conducted when a blade is inserted, pulled out, installed and fixed. The locking device comprises a shell body (1) and a spring (5) which is arranged in the shell body (1) and further comprises a drive mechanism (6) which is arranged in the shell body (1), and a spring bolt (4) which can slide relative to the shell body (1). The locking device is small in operation space when the locking device is automatically locked and unlocked, compact is structure, small in size and particularly capable of being arranged in a thin device.