To surely prevent theft or the like of both a device body and internal parts of a computer by equipping them with a lock means for locking each of the device body and a casing.

This device is a lock device for a personal computer which fixes a casing 2 to a device body 1 with plural screws 2a to 2n, and is equipped with a lock means consisting of a casing lock 12 for locking the casing to the device body and a device body lock 11 for locking the device body to an installment table 3, sensor parts 13a to 13n which detect the detachment of plural screws, a comparator 14 for comparing order of removing the plural screws with a specified order, a control part 15 for having a signal from the comparator control lock of the lock means, a buzzer 16, a timer part 17 for monitoring a screw removal time, and a display device 18 for performing release display of the lock. It is constituted so that the control part releases the locks only when the plural screws are removed within a specified time and that otherwise the buzzer goes off an alarm sound.