To provide a locking device for a computer being capable of locking and unlocking the locking device by a rotary type and being more convenient on a use.

The locking device for the computer contains a body unit, a lock unit, a cylinder unit and a security-cable unit. The body unit has a body case and a ring fitted on the outer peripheral surface of the body case. The lock unit has two hook members fitted into through-holes for a seat section and crossed and can be rocked and two elastic members urging the two hook members at all times so as to close and unite the hook members. The cylinder unit has a lock body fixed into the body case for the body unit and a lock bar mutually opposed to the lock body and being capable of being rotated between a locking place and an unlocking place. The end section of the lock bar is projected from the lock body, and a major axis and a minor axis are defined to the cross section of the lock bar.