A chassis locking apparatus capable of being unlocked spontaneously is used for fixing the chassis in a scanner. The locking apparatus includes a groove interlinking next to the electric socket, a push rod in the groove, and a revolving locking element. By means of the strength of inserting the plug into the socket on the scanner, the push rod is pushed to move along the groove and hit the locking element, which is originally fixed on the chassis, to make the locking element rotate so that the chassis locking apparatus can be unlocked spontaneously. Therefore, no effort is necessary for a user to unlock the chassis locking apparatus by hand before using the scanner, which is convenient and timesaving.